{"segment":[{"time":24,"part":[{"title":"M\u1ed7i kh\u1eb3ng \u0111\u1ecbnh sau \u0110\u00fang hay Sai","title_trans":"","temp":"true_false","correct":[["t","t","f","f","t"]],"list":[{"point":10,"image":"","col_name":["","\u0110\u00fang","Sai"],"arr_ques":["Hai xe kh\u00e1ch c\u00f9ng kh\u1edfi h\u00e0nh m\u1ed9t l\u00fac t\u1eeb $A$ \u0111\u1ebfn $B$ d\u00e0i $120 km$. Xe th\u1ee9 hai \u0111\u1ebfn s\u1edbm h\u01a1n xe th\u1ee9 nh\u1ea5t $30$ ph\u00fat. N\u1ebfu g\u1ecdi th\u1eddi gian c\u1ee7a xe th\u1ee9 nh\u1ea5t l\u00e0 $x$ th\u00ec bi\u1ec3u th\u1ee9c bi\u1ec3u di\u1ec5n v\u1eadn t\u1ed1c xe th\u1ee9 hai theo $x$ l\u00e0: $\\dfrac {120}{x-\\dfrac {1} {2}}$","M\u1ed9t h\u00ecnh vu\u00f4ng c\u00f3 chu vi l\u00e0 $16x\\,cm$. Bi\u1ec3u th\u1ee9c bi\u1ec3u di\u1ec5n di\u1ec7n t\u00edch c\u1ee7a h\u00ecnh vu\u00f4ng khi t\u0103ng m\u1ed7i c\u1ea1nh th\u00eam $5 cm$ l\u00e0: $(4x+5)^2$ ","M\u1ed9t v\u00f2i n\u01b0\u1edbc ch\u1ea3y m\u1ed9t m\u00ecnh $2$ gi\u1edd th\u00ec \u0111\u1ea7y b\u1ec3. N\u1ebfu ch\u1ea3y trong $40$ ph\u00fat th\u00ec v\u00f2i n\u01b0\u1edbc \u0111\u00f3 ch\u1ea3y \u0111\u01b0\u1ee3c $\\dfrac {40}{2}$ b\u1ec3.","Hi\u1ec7n nay con $x$ tu\u1ed5i. Hai n\u0103m n\u1eefa tu\u1ed5i con b\u1eb1ng $\\dfrac {1}{2}$ tu\u1ed5i b\u1ed1. Hi\u1ec7n nay tu\u1ed5i b\u1ed1 l\u00e0 $2x-2$.","M\u1ed9t khu v\u01b0\u1eddn h\u00ecnh ch\u1eef nh\u1eadt c\u00f3 chu vi $120m$ v\u00e0 di\u1ec7n t\u00edch $900 m^2$. T\u00ednh chi\u1ec1u d\u00e0i v\u00e0 chi\u1ec1u r\u1ed9ng c\u1ee7a khu v\u01b0\u1eddn. <br\/>N\u1ebfu g\u1ecdi chi\u1ec1u d\u00e0i khu v\u01b0\u1eddn l\u00e0 $x$ th\u00ec ph\u01b0\u01a1ng tr\u00ecnh bi\u1ec3u th\u1ecb b\u00e0i to\u00e1n t\u00ecm chi\u1ec1u d\u00e0i khu v\u01b0\u1eddn l\u00e0:<br\/> $x(60-x)=900$ ho\u1eb7c $\\left[x+\\dfrac {900}{x}\\right].2=120$"],"explain":[" <span class='basic_left'>\u0110\u00fang. V\u00ec<br\/> \u0110\u1ed5i $30$ ph\u00fat $=\\dfrac {1}{2}$ gi\u1edd.<br\/>V\u00ec xe th\u1ee9 hai \u0111\u1ebfn s\u1edbm h\u01a1n xe th\u1ee9 nh\u1ea5t $30$ ph\u00fat n\u00ean th\u1eddi gian xe th\u1ee9 hai \u00edt h\u01a1n xe th\u1ee9 nh\u1ea5t l\u00e0 $30$ ph\u00fat .<br\/>Do v\u1eady th\u1eddi gian xe th\u1ee9 hai l\u00e0: $x- \\dfrac {1}{2}$ (gi\u1edd)<br\/>V\u1eady v\u1eadn t\u1ed1c c\u1ee7a xe th\u1ee9 hai l\u00e0 $\\dfrac {120}{x-\\dfrac {1}{2}}\\,(km\/h)$<\/span>","<br\/><span class='basic_left'> \u0110\u00fang. V\u00ec <br\/>H\u00ecnh vu\u00f4ng c\u00f3 chu vi l\u00e0 $16x\\,cm$ n\u00ean \u0111\u1ed9 d\u00e0i m\u1ed7i c\u1ea1nh l\u00e0 $4x\\,cm$<br\/>Khi t\u0103ng m\u1ed7i c\u1ea1nh th\u00eam $5 cm$ th\u00ec \u0111\u1ed9 d\u00e0i m\u1ed7i c\u1ea1nh l\u00e0 $4x+5\\,(cm)$.<br\/>Di\u1ec7n t\u00edch c\u1ee7a h\u00ecnh vu\u00f4ng sau khi t\u0103ng \u0111\u1ed9 d\u00e0i c\u1ea1nh l\u00e0 $(4x+5)^2\\,(cm^2)$<\/span>","<br\/><span class='basic_left'> Sai. V\u00ec <br\/>\u0110\u1ed5i $40$ ph\u00fat $= \\dfrac {2}{3}$ gi\u1edd.<br\/>M\u1ed9t gi\u1edd v\u00f2i ch\u1ea3y \u0111\u01b0\u1ee3c $\\dfrac {2}{6}=\\dfrac{1}{3}$ b\u1ec3.<\/span>","<br\/><span class='basic_left'> Sai. V\u00ec<br\/> Tu\u1ed5i con hai n\u0103m n\u1eefa l\u00e0 $x+2$.<br\/>Tu\u1ed5i b\u1ed1 hai n\u0103m n\u1eefa l\u00e0 $2(x+2)$<br\/>Tu\u1ed5i b\u1ed1 hi\u1ec7n nay l\u00e0 $2(x+2)-2=2x+2$<\/span>","<br\/><span class='basic_left'>\u0110\u00fang. V\u00ec<br\/>G\u1ecdi chi\u1ec1u d\u00e0i m\u1ea3nh v\u01b0\u1eddn l\u00e0 $x$ ($m, x>0$)<br\/> <b>C\u00e1ch 1:<\/b> Chi\u1ec1u r\u1ed9ng m\u1ea3nh v\u01b0\u1eddn l\u00e0 <br\/>$120:2-x=60-x\\,(m)$<br\/>V\u00ec di\u1ec7n t\u00edch m\u1ea3nh v\u01b0\u1eddn l\u00e0 $900m^2$ n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh: $x(60-x)=900$<br\/> <b>C\u00e1ch 2:<\/b> Chi\u1ec1u r\u1ed9ng m\u1ea3nh v\u01b0\u1eddn l\u00e0 $\\dfrac {900}{x}\\,(m)$<br\/>V\u00ec m\u1ea3nh v\u01b0\u1eddn c\u00f3 chu vi l\u00e0 $120m$ n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh <br\/>$\\left[x+\\dfrac{900}{x}\\right].2=120$<\/span>"]}]}],"id_ques":981},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["50"]]],"list":[{"point":10,"width":50,"type_input":"","input_hint":"","ques":"<span class='basic_left'>B\u1ea1n H\u1ea3i \u0111\u1ed1 b\u1ea1n Nam: \u201cN\u1ebfu b\u1ea1n l\u1ea5y $5$ l\u1ea7n tu\u1ed5i b\u1ed1 m\u00ecnh sau $5$ n\u0103m n\u1eefa tr\u1eeb \u0111i $5$ l\u1ea7n tu\u1ed5i c\u1ee7a b\u1ed1 m\u00ecnh c\u00e1ch \u0111\u00e2y $5$ n\u0103m s\u1ebd \u0111\u01b0\u1ee3c m\u1ed9t s\u1ed1 b\u1eb1ng s\u1ed1 tu\u1ed5i c\u1ee7a b\u1ed1 m\u00ecnh hi\u1ec7n nay. \u0110\u1ed1 b\u1ea1n n\u0103m nay b\u1ed1 m\u00ecnh bao nhi\u00eau tu\u1ed5i?\u201d<br\/><b>\u0110\u00e1p s\u1ed1:<\/b> $\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}$(tu\u1ed5i)<\/span>","hint":"G\u1ecdi tu\u1ed5i c\u1ee7a b\u1ed1 H\u1ea3i hi\u1ec7n nay l\u00e0 \u1ea9n $x$.","explain":"<span class='basic_left'><center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/daiso/bai21/lv3/img\/D8_B21K1.3.png' \/><\/center>G\u1ecdi tu\u1ed5i c\u1ee7a b\u1ed5 H\u1ea3i hi\u1ec7n nay l\u00e0 $x$ (tu\u1ed5i, $x\\in \\mathbb N^*$).<br\/>S\u1ed1 tu\u1ed5i c\u1ee7a b\u1ed1 H\u1ea3i $5$ n\u0103m n\u1eefa l\u00e0 $x+5$ tu\u1ed5i.<br\/>S\u1ed1 tu\u1ed5i b\u1ed1 H\u1ea3i c\u00e1ch \u0111\u00e2y $5$ n\u0103m l\u00e0 $x-5$ tu\u1ed5i.<br\/>Theo d\u1eef ki\u1ec7n b\u00e0i to\u00e1n ta c\u00f3: $5(x+5)-5(x-5)=x\\\\ \\Leftrightarrow 5x+25-5x+25=x\\\\ \\Leftrightarrow x=50\\,\\,\\,\\text{(th\u1ecfa m\u00e3n)}$<br\/>V\u1eady hi\u1ec7n nay b\u1ed1 H\u1ea3i $50$ tu\u1ed5i.<br\/><span class='basic_pink'>V\u1eady s\u1ed1 c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $50$<\/span><br\/><\/span>"}]}],"id_ques":982},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["10"]]],"list":[{"point":10,"width":50,"type_input":"","input_hint":"","ques":"M\u1ed9t ph\u00f2ng h\u1ecdc c\u00f3 m\u1ed9t s\u1ed1 d\u00e3y gh\u1ebf, c\u00f3 t\u1ed5ng c\u1ed9ng $40$ ch\u1ed7 ng\u1ed3i. Do ph\u1ea3i x\u1ebfp $55$ ch\u1ed7 n\u00ean ng\u01b0\u1eddi ta ph\u1ea3i k\u00ea th\u00eam $1$ d\u00e3y gh\u1ebf v\u00e0 m\u1ed7i d\u00e3y gh\u1ebf ng\u1ed3i th\u00eam $1$ ch\u1ed7. H\u1ecfi l\u00fac \u0111\u1ea7u c\u00f3 bao nhi\u00eau d\u00e3y gh\u1ebf trong l\u1edbp h\u1ecdc? (Bi\u1ebft r\u1eb1ng m\u1ed7i d\u00e3y gh\u1ebf ng\u1ed3i kh\u00f4ng qu\u00e1 $5$ ng\u01b0\u1eddi)<br\/><b>\u0110\u00e1p s\u1ed1:<\/b> $\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}$(d\u00e3y gh\u1ebf)","hint":"G\u1ecdi s\u1ed1 d\u00e3y gh\u1ebf ban \u0111\u1ea7u l\u00e0 $x$","explain":"<span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn:<\/span><br\/><b>B\u01b0\u1edbc 1:<\/b> G\u1ecdi s\u1ed1 d\u00e3y gh\u1ebf ban \u0111\u1ea7u l\u00e0 \u1ea9n.<br\/><b>B\u01b0\u1edbc 2:<\/b> Bi\u1ec3u di\u1ec5n s\u1ed1 ch\u1ed7 ng\u1ed3i ban \u0111\u1ea7u theo \u1ea9n.<br\/><b>B\u01b0\u1edbc 3:<\/b> Bi\u1ec3u di\u1ec5n ch\u1ed7 ng\u1ed3i sau khi th\u00eam d\u00e3y gh\u1ebf theo \u1ea9n<br\/><b>B\u01b0\u1edbc 4:<\/b> L\u1eadp ph\u01b0\u01a1ng tr\u00ecnh v\u00e0 gi\u1ea3i ph\u01b0\u01a1ng tr\u00ecnh.<br\/>L\u1eadp b\u1ea3ng:<br\/><table><tr><th><\/th><th>S\u1ed1 d\u00e3y<\/th><th>S\u1ed1 ch\u1ed7 ng\u1ed3i<\/th><th>S\u1ed1 ch\u1ed7 m\u1ed7i d\u00e3y<\/th><\/tr><tr><td>Ban \u0111\u1ea7u<\/td><td>$x$<\/td><td>$44$<\/td><td>$\\dfrac {40}{x}$<\/td><\/tr><tr><td>Khi l\u00e0m vi\u1ec7c<\/td><td>$x+1$<\/td><td>$55$<\/td><td>$\\dfrac {55}{x-1}$<\/td><\/tr><\/table><br\/><span class='basic_green'>B\u00e0i gi\u1ea3i<\/span><br\/>G\u1ecdi s\u1ed1 d\u00e3y gh\u1ebf ban \u0111\u1ea7u l\u00e0 $x$ (d\u00e3y gh\u1ebf, $x\\in \\mathbb N^*, \\,x>8$)<br\/>V\u00ec c\u00f3 t\u1ed5ng c\u1ed9ng $40$ ch\u1ed7 ng\u1ed3i n\u00ean s\u1ed1 ch\u1ed7 ng\u1ed3i \u1edf m\u1ed7i d\u00e3y gh\u1ebf l\u00e0 $\\dfrac {40}{x}$ (ch\u1ed7)<br\/>Sau khi th\u00eam $1$ d\u00e3y gh\u1ebf th\u00ec s\u1ed1 d\u00e3y gh\u1ebf m\u1edbi l\u00e0 $x+1$ (d\u00e3y gh\u1ebf)<br\/>Khi \u0111\u00f3, s\u1ed1 ch\u1ed7 ng\u1ed3i m\u1ed7i d\u00e3y l\u00e0 $\\dfrac {55}{x+1}$ (ch\u1ed7)<br\/>V\u00ec m\u1ed7i d\u00e3y ph\u1ea3i ng\u1ed3i th\u00eam $1$ ch\u1ed7 n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh :<br\/>$\\dfrac {55}{x+1}-\\dfrac {40}{x}=1\\\\ \\Leftrightarrow 55x-40(x+1)=x(x+1)\\\\ \\Leftrightarrow x^2-14x+40=0\\\\ \\Leftrightarrow x^2-10x-4x+40=0\\\\ \\Leftrightarrow x(x-10)-4(x-10)=0\\\\ \\Leftrightarrow (x-10)(x-4)=0\\\\ \\Leftrightarrow \\left[\\begin{align}&x=10\\,\\,\\,\\text{(th\u1ecfa m\u00e3n)}\\\\&x=4\\,\\,\\,\\text{(lo\u1ea1i)}\\\\ \\end{align}\\right.$<br\/>V\u1eady ban \u0111\u1ea7u l\u1edbp h\u1ecdc c\u00f3 $10$ d\u00e3y gh\u1ebf<br\/><span class='basic_pink'>V\u1eady s\u1ed1 c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $10$<\/span><br\/><\/span>"}]}],"id_ques":983},{"time":24,"part":[{"title":"L\u1ef1a ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang nh\u1ea5t","title_trans":"","temp":"multiple_choice","correct":[[1]],"list":[{"point":10,"ques":"<center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/daiso/bai21/lv3/img\/12.jpg' \/><\/center>M\u1ed9t ng\u01b0\u1eddi \u0111i t\u1eeb $A$ \u0111\u1ebfn $B$ v\u1edbi v\u1eadn t\u1ed1c $24 km\/h$ r\u1ed3i \u0111i ti\u1ebfp \u0111\u1ebfn $C$ v\u1edbi v\u1eadn t\u1ed1c $32 km\/h$. T\u00ednh qu\u00e3ng \u0111\u01b0\u1eddng $AB$ bi\u1ebft qu\u00e3ng \u0111\u01b0\u1eddng $AB$ d\u00e0i h\u01a1n qu\u00e3ng \u0111\u01b0\u1eddng $BC$ l\u00e0 $6 km$ v\u00e0 v\u1eadn t\u1ed1c trung b\u00ecnh tr\u00ean c\u1ea3 qu\u00e3ng \u0111\u01b0\u1eddng l\u00e0 $27 km\/h.$","select":["A. $30\\,km$","B. $40\\,km$","C. $50\\,km$"],"hint":"V\u1eadn t\u1ed1c trung b\u00ecnh $=$ T\u1ed5ng qu\u00e3ng \u0111\u01b0\u1eddng \u0111i \u0111\u01b0\u1ee3c $:$ t\u1ed5ng th\u1eddi gian \u0111i h\u1ebft qu\u00e3ng \u0111\u01b0\u1eddng.<br\/>Bi\u1ec3u di\u1ec5n th\u1eddi gian ng\u01b0\u1eddi \u0111\u00f3 \u0111i tr\u00ean t\u1eebng \u0111o\u1ea1n \u0111\u01b0\u1eddng v\u00e0 tr\u00ean c\u1ea3 \u0111o\u1ea1n \u0111\u01b0\u1eddng $AB$","explain":" <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/daiso/bai21/lv3/img\/D8_B21K1.1.png' \/><\/center><span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn:<\/span><br\/><b>B\u01b0\u1edbc 1:<\/b> G\u1ecdi chi\u1ec1u d\u00e0i qu\u00e3ng \u0111\u01b0\u1eddng $AB$ l\u00e0 \u1ea9n<br\/><b>B\u01b0\u1edbc 2:<\/b> Bi\u1ec3u di\u1ec5n th\u1eddi gian ng\u01b0\u1eddi \u0111\u00f3 \u0111i tr\u00ean qu\u00e3ng \u0111\u01b0\u1eddng $AB$ v\u00e0 $BC$ theo \u1ea9n.<br\/><b>B\u01b0\u1edbc 3:<\/b> Bi\u1ec3u di\u1ec5n th\u1eddi gian ng\u01b0\u1eddi \u0111\u00f3 \u0111i tr\u00ean c\u1ea3 qu\u00e3ng \u0111\u01b0\u1eddng $AC$ theo \u1ea9n <br\/><b>B\u01b0\u1edbc 4:<\/b> L\u1eadp ph\u01b0\u01a1ng tr\u00ecnh v\u00e0 gi\u1ea3i.<br\/>L\u1eadp b\u1ea3ng:<br\/><table><tr><th><\/th><th>Qu\u00e3ng \u0111\u01b0\u1eddng ($km$)<\/th><th>V\u1eadn t\u1ed1c $(km\/h)$<\/th><th>Th\u1eddi gian (gi\u1edd)<\/th><\/tr><tr><td>Tr\u00ean $AB$<\/td><td>$x$<\/td><td>$24$<\/td><td>$\\dfrac{x}{24}$<\/td><\/tr><tr><td>Tr\u00ean $BC$<\/td><td>$x-6$<\/td><td>$32$<\/td><td>$\\dfrac{x-6}{32}$<\/td><\/tr><tr><td>Tr\u00ean $AC$<\/td><td>$2x-6$<\/td><td>$27$<\/td><td>$\\dfrac{2x-6}{27}$<\/td><\/tr><\/table><br\/><span class='basic_green'>B\u00e0i gi\u1ea3i<\/span><br\/>G\u1ecdi chi\u1ec1u d\u00e0i qu\u00e3ng \u0111\u01b0\u1eddng $AB$ l\u00e0 $x$ $(km, x > 0)$ <br\/> Qu\u00e3ng \u0111\u01b0\u1eddng $BC$ d\u00e0i l\u00e0 $x-6$ $(km)$<br\/>Qu\u00e3ng \u0111\u01b0\u1eddng $AC$ d\u00e0i l\u00e0 $2x-6$ $(km)$<br\/>Th\u1eddi gian ng\u01b0\u1eddi \u0111\u00f3 \u0111i tr\u00ean qu\u00e3ng \u0111\u01b0\u1eddng $AB$ l\u00e0 $\\dfrac {x}{24}$ (gi\u1edd)<br\/>Th\u1eddi gian ng\u01b0\u1eddi \u0111\u00f3 \u0111i h\u1ebft qu\u00e3ng \u0111\u01b0\u1eddng $BC$ l\u00e0 $\\dfrac {x-6}{32}$ (gi\u1edd)<br\/>Th\u1eddi gian \u0111i h\u1ebft qu\u00e3ng \u0111\u01b0\u1eddng $AC$ t\u00ednh theo v\u1eadn t\u1ed1c trung b\u00ecnh l\u00e0 $\\dfrac {2x-6}{27}\\,(km\/h)$<br\/>Ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh:<br\/> $\\dfrac {x}{24}+\\dfrac {x-6}{32}=\\dfrac {2x-6}{27}\\\\ \\Leftrightarrow 36x+27(x-6)=32(2x-6)\\\\ \\Leftrightarrow x=30\\,\\,\\text {(th\u1ecfa m\u00e3n)}$<br\/><span class='basic_pink'>V\u1eady \u0111\u00e1p \u00e1n \u0111\u00fang l\u00e0 A<\/span><br\/><b>Ghi nh\u1edb: <\/b>V\u1eadn t\u1ed1c trung b\u00ecnh $=$ T\u1ed5ng qu\u00e3ng \u0111\u01b0\u1eddng \u0111i \u0111\u01b0\u1ee3c $:$ t\u1ed5ng th\u1eddi gian \u0111i h\u1ebft qu\u00e3ng \u0111\u01b0\u1eddng.<\/span>","column":3}]}],"id_ques":984},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["2"]]],"list":[{"point":10,"width":50,"type_input":"","ques":"<center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/daiso/bai21/lv3/img\/11.jpg' \/><\/center>M\u1ed9t \u00f4t\u00f4 ph\u1ea3i \u0111i qu\u00e3ng \u0111\u01b0\u1eddng $AB$ d\u00e0i $60km$ trong m\u1ed9t th\u1eddi gian nh\u1ea5t \u0111\u1ecbnh. \u00d4t\u00f4 \u0111i n\u1eeda \u0111\u1ea7u qu\u00e3ng \u0111\u01b0\u1eddng v\u1edbi v\u1eadn t\u1ed1c h\u01a1n d\u1ef1 \u0111\u1ecbnh $10km\/h$ v\u00e0 \u0111i n\u1eeda sau qu\u00e3ng \u0111\u01b0\u1eddng v\u1edbi v\u1eadn t\u1ed1c k\u00e9m h\u01a1n d\u1ef1 \u0111\u1ecbnh $6km\/h$. Bi\u1ebft \u00f4t\u00f4 \u0111\u1ebfn $B$ \u0111\u00fang th\u1eddi gian \u0111\u00e3 \u0111\u1ecbnh. T\u00ednh th\u1eddi gian \u00f4 t\u00f4 d\u1ef1 \u0111\u1ecbnh \u0111i qu\u00e3ng \u0111\u01b0\u1eddng $AB.$<br\/><b>\u0110\u00e1p s\u1ed1: <\/b> $\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}$(gi\u1edd)","hint":"G\u1ecdi v\u1eadn t\u1ed1c d\u1ef1 \u0111\u1ecbnh c\u1ee7a \u00f4 t\u00f4 l\u00e0 \u1ea9n s\u1ed1. ","explain":"<span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn<\/span><br\/><b>B\u01b0\u1edbc 1:<\/b> G\u1ecdi v\u1eadn t\u1ed1c d\u1ef1 \u0111\u1ecbnh c\u1ee7a \u00f4 t\u00f4 l\u00e0 \u1ea9n s\u1ed1.<br\/><b>B\u01b0\u1edbc 2:<\/b> Bi\u1ec3u di\u1ec5n th\u1eddi gian d\u1ef1 \u0111\u1ecbnh v\u00e0 th\u1eddi gian th\u1ee9c t\u1ebf theo \u1ea9n s\u1ed1<br\/><b>B\u01b0\u1edbc 3:<\/b> L\u1eadp ph\u01b0\u01a1ng tr\u00ecnh v\u00e0 gi\u1ea3i<br\/><b>B\u01b0\u1edbc 4:<\/b> T\u00ecm th\u1eddi gian d\u1ef1 \u0111\u1ecbnh r\u1ed3i k\u1ebft lu\u1eadn.<br\/>L\u1eadp b\u1ea3ng:<br\/><table><tr><th><\/th><th>D\u1ef1 \u0111\u1ecbnh<\/th><th>N\u1eeda \u0111\u01b0\u1eddng \u0111\u1ea7u<\/th><th>N\u1eeda \u0111\u01b0\u1eddng sau<\/th><\/tr><tr><td>Qu\u00e3ng \u0111\u01b0\u1eddng ($km$)<\/td><td>$60$<\/td><td>$30$<\/td><td>$30$<\/td><\/tr><tr><td>V\u1eadn t\u1ed1c<\/td><td>$x$<\/td><td>$x+10$<\/td><td>$x-6$<\/td><\/tr><tr><td>Th\u1eddi gian<\/td><td>$\\dfrac{60}{x}$<\/td><td>$\\dfrac{30}{x+10}$<\/td><td>$\\dfrac{30}{x-6}$<\/td><\/tr><\/table><span class='basic_green'>B\u00e0i gi\u1ea3i<\/span><br\/> G\u1ecdi v\u1eadn t\u1ed1c d\u1ef1 \u0111\u1ecbnh c\u1ee7a \u00f4 t\u00f4 l\u00e0 $x$ ($km\/h$, $x>0$)<br\/>Th\u1eddi gian \u00f4 t\u00f4 \u0111\u1ecbnh \u0111i h\u1ebft qu\u00e3ng \u0111\u01b0\u1eddng $AB$ l\u00e0 $\\dfrac{60}{x}$ (gi\u1edd)<br\/>\u00d4 t\u00f4 \u0111i n\u1eeda qu\u00e3ng \u0111\u01b0\u1eddng \u0111\u1ea7u ($=30\\,km$) v\u1edbi v\u1eadn t\u1ed1c l\u00e0 $x+10$ ($km\/h$)<br\/>Th\u1eddi gian \u00f4 t\u00f4 \u0111i h\u1ebft n\u1eefa qu\u00e3ng \u0111\u01b0\u1eddng \u0111\u1ea7u l\u00e0 $\\dfrac{30}{x+10}$ (gi\u1edd)<br\/>\u00d4 t\u00f4 \u0111i n\u1eeda qu\u00e3ng \u0111\u01b0\u1eddng sau v\u1edbi v\u1eadn t\u1ed1c $x-6$ ($km\/h$)<br\/>Th\u1eddi gian \u00f4 t\u00f4 \u0111i h\u1ebft n\u1eefa qu\u00e3ng \u0111\u01b0\u1eddng sau l\u00e0 $\\dfrac {x}{x-6}$ (gi\u1edd)<br\/>V\u00ec \u00f4 t\u00f4 \u0111\u1ebfn $B$ \u0111\u00fang th\u1eddi gian quy \u0111\u1ecbnh n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh:<br\/>$\\dfrac{60}{x}=\\dfrac{30}{x+10}+\\dfrac {30}{x-6}\\\\ \\Leftrightarrow \\dfrac{2(x+10)(x-6)}{x(x+10)(x-6)}=\\dfrac{x(x-6)}{x(x+10)(x-6)}+\\dfrac {x(x+10)}{x(x+10)(x-6)}\\\\ \\Rightarrow 2(x^2+4x-60)=x^2-6x+x^2+10x\\\\ \\Leftrightarrow 4x=120\\\\ \\Leftrightarrow x=30\\,\\,\\text{(th\u1ecfa m\u00e3n)}$<br\/>V\u1eady th\u1eddi gian \u00f4 t\u00f4 d\u1ef1 \u0111\u1ecbnh \u0111i h\u1ebft qu\u00e3ng \u0111\u01b0\u1eddng $AB$ l\u00e0 $\\dfrac {60}{30}=2$ (gi\u1edd) <br\/><span class='basic_pink'>V\u1eady s\u1ed1 c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $2$ <\/span><\/span>"}]}],"id_ques":985},{"time":24,"part":[{"title":"L\u1ef1a ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang nh\u1ea5t","title_trans":"","temp":"multiple_choice","correct":[[4]],"list":[{"point":10,"ques":"M\u1ed9t ca n\u00f4 xu\u00f4i d\u00f2ng t\u1eeb $A$ \u0111\u1ebfn $B$ h\u1ebft $3$ gi\u1edd. Sau \u0111\u00f3, ca n\u00f4 tr\u1edf l\u1ea1i ng\u01b0\u1ee3c t\u1eeb $B$ \u0111\u1ebfn b\u00ean $C$ c\u00e1ch $A$ m\u1ed9t kho\u1ea3ng b\u1eb1ng $\\dfrac {1}{3}AB$ h\u1ebft $2$ gi\u1edd $24$ ph\u00fat. T\u00ednh \u0111\u1ed9 d\u00e0i \u0111o\u1ea1n s\u00f4ng $AB$ bi\u1ebft m\u1ed9t kh\u00f3m b\u00e8o tr\u00f4i tr\u00ean s\u00f4ng \u0111\u00f3 $12$ ph\u00fat \u0111\u01b0\u1ee3c $400m.$","select":["A. $36\\,km$","B. $20,57\\,km$","C. $4 \\,km$","D. $72\\,km$"],"hint":"V\u1eadn t\u1ed1c ca n\u00f4 kh\u00f4ng \u0111\u1ed5i.<br\/>V\u1eadn t\u1ed1c d\u00f2ng n\u01b0\u1edbc $=$ v\u1eadn t\u1ed1c c\u1ee7a nh\u00f3m b\u00e8o.","explain":" <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/daiso/bai21/lv3/img\/D8_B21K1.2.png' \/><\/center><span class='basic_left'>\u0110\u1ed5i: $12$ ph\u00fat $=\\dfrac{1}{5}$ gi\u1edd; $2$ gi\u1edd $24$ ph\u00fat $= \\dfrac{12}{5}$ gi\u1edd<br\/>V\u1eadn t\u1ed1c d\u00f2ng n\u01b0\u1edbc $=$ v\u1eadn t\u1ed1c c\u1ee7a nh\u00f3m b\u00e8o $= 0,4:\\dfrac {1}{5}=2 \\,km\/h$<br\/>G\u1ecdi \u0111\u1ed9 d\u00e0i \u0111o\u1ea1n s\u00f4ng $AB$ l\u00e0 $x$ ($km,\\,x > 0$). <br\/>V\u1eadn t\u1ed1c c\u1ee7a ca n\u00f4 khi xu\u00f4i d\u00f2ng t\u1eeb $A$ \u0111\u1ebfn $B$ l\u00e0 $\\dfrac {x}{3}$ ($km\/h$)<br\/>Qu\u00e3ng s\u00f4ng ca n\u00f4 \u0111i ng\u01b0\u1ee3c d\u00f2ng l\u00e0 $x-\\dfrac {1}{3}x=\\dfrac{2}{3}x$ ($km$)<br\/>V\u1eadn t\u1ed1c ca n\u00f4 \u0111i ng\u01b0\u1ee3c d\u00f2ng l\u00e0 $\\dfrac {2}{3}x:\\dfrac {12}{5}=\\dfrac {5}{18}x$ <br\/>V\u00ec v\u1eadn t\u1ed1c ca n\u00f4 kh\u00f4ng \u0111\u1ed5i n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh:<br\/>$\\dfrac {x}{3}-2=\\dfrac {5}{18}x+2\\\\ \\Leftrightarrow \\dfrac {x}{3}=\\dfrac {5}{18}x+4\\\\ \\Leftrightarrow 6x=5x+72\\\\ \\Leftrightarrow x=72\\,\\,\\text {(km)}$<br\/><span class='basic_pink'>V\u1eady \u0111\u00e1p \u00e1n \u0111\u00fang l\u00e0 D<\/span><br\/><b> Ghi nh\u1edb:<\/b> V\u1eadn t\u1ed1c d\u00f2ng n\u01b0\u1edbc $=$ v\u1eadn t\u1ed1c c\u1ee7a nh\u00f3m b\u00e8o tr\u00f4i tr\u00ean s\u00f4ng.<br\/>$v=\\dfrac{s}{t}$ (trong \u0111\u00f3, $s$ l\u00e0 qu\u00e3ng \u0111\u01b0\u1eddng, $v$ l\u00e0 v\u1eadn t\u1ed1c, $t$ l\u00e0 th\u1eddi gian)<\/span>","column":2}]}],"id_ques":986},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["1234"]]],"list":[{"point":10,"width":50,"type_input":"","ques":"T\u00ecm m\u1ed9t s\u1ed1 t\u1ef1 nhi\u00ean c\u00f3 $4$ ch\u1eef s\u1ed1. Bi\u1ebft n\u1ebfu vi\u1ebft th\u00eam ch\u1eef s\u1ed1 $5$ v\u00e0o b\u00ean tr\u00e1i th\u00ec \u0111\u01b0\u1ee3c m\u1ed9t s\u1ed1 m\u1edbi l\u1edbn h\u01a1n s\u1ed1 \u0111\u00f3 khi vi\u1ebft th\u00eam ch\u1eef s\u1ed1 $5$ v\u00e0o b\u00ean ph\u1ea3i l\u00e0 $38889$ \u0111\u01a1n v\u1ecb.<br\/><b> \u0110\u00e1p s\u1ed1: <\/b> _input_ ","hint":"G\u1ecdi s\u1ed1 c\u1ea7n t\u00ecm c\u00f3 d\u1ea1ng $\\overline{abcd}$. ","explain":"<span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn<\/span><br\/><b>B\u01b0\u1edbc 1:<\/b> G\u1ecdi s\u1ed1 c\u1ea7n t\u00ecm c\u00f3 d\u1ea1ng $\\overline {abcd}$<br\/><b>B\u01b0\u1edbc 2:<\/b> B\u01b0\u1edbc di\u1ec5n hai s\u1ed1 m\u1edbi theo s\u1ed1 ban \u0111\u1ea7u<br\/><b>B\u01b0\u1edbc 3:<\/b> L\u1eadp ph\u01b0\u01a1ng tr\u00ecnh.<br\/><b>B\u01b0\u1edbc 4:<\/b> \u00c1p d\u1ee5ng ph\u01b0\u01a1ng ph\u00e1p ph\u00e2n t\u00edch c\u1ea5u t\u1ea1o s\u1ed1 \u0111\u1ec3 gi\u1ea3i ph\u01b0\u01a1ng tr\u00ecnh.<br\/><span class='basic_green'>B\u00e0i gi\u1ea3i<\/span><br\/>G\u1ecdi s\u1ed1 ph\u1ea3i t\u00ecm l\u00e0 $\\overline{abcd}$. ($a \\ne 0$)<br\/>Vi\u1ebft th\u00eam ch\u1eef s\u1ed1 $5$ v\u00e0o b\u00ean tr\u00e1i \u0111\u01b0\u1ee3c m\u1ed9t s\u1ed1 c\u00f3 $5$ ch\u1eef s\u1ed1 m\u1edbi l\u00e0: $\\overline{5abcd}$.<br\/>Vi\u1ebft th\u00eam ch\u1eef s\u1ed1 $5$ v\u00e0o b\u00ean ph\u1ea3i \u0111\u01b0\u1ee3c m\u1ed9t s\u1ed1 c\u00f3 $5$ ch\u1eef s\u1ed1 m\u1edbi l\u00e0: $\\overline{abcd5}$.<br\/>Theo gi\u1ea3 thi\u1ebft, ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh: <br\/>$\\begin{aligned}& \\overline{5abcd}-\\overline{abcd5}=38889 \\\\ & \\Leftrightarrow 50000+\\overline{abcd}-(\\overline{abcd0}+5)=38889 \\\\ & \\Leftrightarrow\\overline{abcd}-10\\overline{abcd}=-50000+5+38889 \\\\ & \\Leftrightarrow -9\\overline{abcd}=-11106 \\\\ & \\Leftrightarrow \\overline{abcd}=1234 \\\\ \\end{aligned}$<br\/><span class='basic_pink'>V\u1eady s\u1ed1 ph\u1ea3i t\u00ecm l\u00e0 $1234$<\/span><br\/><b> Nh\u1eadn x\u00e9t: <\/b> Gi\u1ed1ng nh\u01b0 b\u00e0i to\u00e1n gi\u1ea3i ph\u01b0\u01a1ng tr\u00ecnh b\u1eb1ng c\u00e1ch \u0111\u1eb7t \u1ea9n ph\u1ee5: Trong ph\u1ea7n gi\u1ea3i c\u1ee7a ph\u01b0\u01a1ng tr\u00ecnh tr\u00ean, ta coi $\\overline{abcd}$ l\u00e0 \u1ea9n c\u1ea7n t\u00ecm.<\/span>"}]}],"id_ques":987},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["20"],["30"]]],"list":[{"point":10,"width":50,"type_input":"","ques":"<span class='basic_left'>Hai v\u00f2i n\u01b0\u1edbc c\u00f9ng ch\u1ea3y v\u00e0o b\u1ec3 th\u00ec trong $12$ ph\u00fat \u0111\u1ea7y b\u1ec3. N\u1ebfu m\u1ed9t m\u00ecnh v\u00f2i $1$ ch\u1ea3y trong $10$ ph\u00fat, v\u00f2i $2$ ch\u1ea3y trong $12$ ph\u00fat th\u00ec \u0111\u01b0\u1ee3c $90\\%$ b\u1ec3. H\u1ecfi n\u1ebfu m\u1ed7i v\u00f2i ch\u1ea3y m\u1ed9t m\u00ecnh th\u00ec sau bao l\u00e2u \u0111\u1ea7y b\u1ec3?<br\/><b> \u0110\u00e1p s\u1ed1: <\/b><br\/> V\u00f2i $1$: _input_ (ph\u00fat); V\u00f2i $2$: _input_ (ph\u00fat)<\/span>","hint":"\u0110\u00e2y l\u00e0 b\u00e0i to\u00e1n n\u0103ng su\u1ea5t. T\u00ednh th\u1eddi gian theo ph\u00fat.","explain":"<span class='basic_left'>G\u1ecdi th\u1eddi gian v\u00f2i m\u1ed9t ch\u1ea3y m\u1ed9t m\u00ecnh \u0111\u1ea7y b\u1ec3 l\u00e0 $x$ (ph\u00fat, $x>12$).<br\/>M\u1ed9t ph\u00fat v\u00f2i m\u1ed9t ch\u1ea3y \u0111\u01b0\u1ee3c $\\dfrac {1}{x}$ b\u1ec3.<br\/>$10$ ph\u00fat v\u00f2i $1$ ch\u1ea3y \u0111\u01b0\u1ee3c l\u00e0 $\\dfrac {10}{x}$ (b\u1ec3)<br\/>V\u00ec hai v\u00f2i c\u00f9ng ch\u1ea3y trong $12$ ph\u00fat th\u00ec \u0111\u1ea7y b\u1ec3 n\u00ean $1$ ph\u00fat c\u1ea3 hai v\u00f2i ch\u1ea3y \u0111\u01b0\u1ee3c $\\dfrac {1}{12}$ b\u1ec3.<br\/>Ta c\u00f3, $1$ ph\u00fat v\u00f2i $1$ ch\u1ea3y \u0111\u01b0\u1ee3c $\\dfrac {1}{x}$ b\u1ec3 n\u00ean $1$ ph\u00fat v\u00f2i $2$ ch\u1ea3y \u0111\u01b0\u1ee3c l\u00e0 $\\dfrac {1}{12}-\\dfrac {1}{x}$ (b\u1ec3)<br\/>V\u1eady trong $12$ ph\u00fat v\u00f2i $2$ ch\u1ea3y \u0111\u01b0\u1ee3c $12\\left(\\dfrac{1}{12}-\\dfrac {1}{x}\\right)$ (b\u1ec3)<br\/>V\u00ec khi \u0111\u00f3, hai v\u00f2i ch\u1ea3y \u0111\u01b0\u1ee3c $90\\%=\\dfrac {9}{10}$ (b\u1ec3) n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh: <br\/>$\\dfrac {10}{x}+12\\left(\\dfrac{1}{12}-\\dfrac {1}{x}\\right)=\\dfrac {9}{10}\\\\ \\Leftrightarrow \\dfrac {10}{x}+1-\\dfrac {12}{x}=\\dfrac {9}{10}\\\\ \\Leftrightarrow \\dfrac {10}{x}-\\dfrac {12}{x}=\\dfrac {-1}{10}\\\\ \\Leftrightarrow \\dfrac {2}{x}=\\dfrac {1}{10}\\\\ \\Leftrightarrow x=20\\,\\,\\text {(th\u1ecfa m\u00e3n)}$ <br\/>V\u1eady m\u1ed9t m\u00ecnh v\u00f2i $1$ ch\u1ea3y trong $20$ ph\u00fat th\u00ec \u0111\u1ea7y b\u1ec3.<br\/>Ta c\u00f3, $1$ ph\u00fat v\u00f2i $2$ ch\u1ea3y \u0111\u01b0\u1ee3c l\u00e0 $\\dfrac{1}{12}-\\dfrac {1}{20}=\\dfrac{1}{30}$ b\u1ec3. Do \u0111\u00f3, v\u00f2i 2 ch\u1ea3y trong $30$ ph\u00fat th\u00ec \u0111\u1ea7y b\u1ec3.<br\/><span class='basic_pink'>V\u1eady c\u00e1c s\u1ed1 c\u1ea7n \u0111i\u1ec1n v\u00e0o ch\u1ed7 tr\u1ed1ng l\u1ea7n l\u01b0\u1ee3t l\u00e0 $20$ v\u00e0 $30$<\/span><br\/> Ngo\u00e0i c\u00e1ch gi\u1ea3i tr\u00ean, th\u00f4ng th\u01b0\u1eddng ch\u00fang ta \u0111\u1ed5i \u0111\u01a1n v\u1ecb th\u1eddi gian ra gi\u1edd r\u1ed3i l\u00e0m nh\u01b0 c\u00e1ch gi\u1ea3i sau:<br\/>\u0110\u1ed5i $10$ ph\u00fat $=\\dfrac {1}{6}$ gi\u1edd.<br\/>$12$ ph\u00fat $= \\dfrac {1}{5}$ gi\u1edd.<br\/>G\u1ecdi th\u1eddi gian v\u00f2i m\u1ed9t ch\u1ea3y m\u1ed9t m\u00ecnh \u0111\u1ea7y b\u1ec3 l\u00e0 $x$ (gi\u1edd).<br\/>M\u1ed9t gi\u1edd v\u00f2i m\u1ed9t ch\u1ea3y \u0111\u01b0\u1ee3c $\\dfrac {1}{x}$ b\u1ec3.<br\/>$\\dfrac {1}{6}$ (gi\u1edd) v\u00f2i $1$ ch\u1ea3y \u0111\u01b0\u1ee3c l\u00e0 $\\dfrac {1}{6x}$ (b\u1ec3)<br\/>V\u00ec hai v\u00f2i c\u00f9ng ch\u1ea3y trong $12$ ph\u00fat th\u00ec \u0111\u1ea7y b\u1ec3 n\u00ean $1$ gi\u1edd c\u1ea3 hai v\u00f2i ch\u1ea3y \u0111\u01b0\u1ee3c $5$ b\u1ec3.<br\/>Ta c\u00f3, $1$ gi\u1edd v\u00f2i $1$ ch\u1ea3y \u0111\u01b0\u1ee3c $\\dfrac {1}{x}$ b\u1ec3 n\u00ean $1$ gi\u1edd v\u00f2i $2$ ch\u1ea3y \u0111\u01b0\u1ee3c l\u00e0 $5-\\dfrac {1}{x}$ (b\u1ec3)<br\/>V\u1eady trong $\\dfrac {1}{5}$ gi\u1edd v\u00f2i $2$ ch\u1ea3y \u0111\u01b0\u1ee3c $\\dfrac {1}{5}\\left(5-\\dfrac {1}{x}\\right)$ (b\u1ec3)<br\/>V\u00ec khi \u0111\u00f3, hai v\u00f2i ch\u1ea3y \u0111\u01b0\u1ee3c $90\\%=\\dfrac {1}{10}$ (b\u1ec3) n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh: <br\/>$\\dfrac {1}{6x}+\\dfrac {1}{5}\\left(5-\\dfrac {1}{x}\\right)= \\dfrac {9}{10}\\\\ \\Leftrightarrow x=\\dfrac {1}{3}$ <br\/>V\u1eady v\u00f2i 1 ch\u1ea3y trong $\\dfrac 1 3 $ gi\u1edd th\u00ec \u0111\u1ea7y b\u1ec3<br\/><b> Nh\u1eadn x\u00e9t:<\/b> \u0110\u1ed1i v\u1edbi m\u1ed9t s\u1ed1 b\u00e0i to\u00e1n d\u1ea1ng n\u0103ng su\u1ea5t \u0111\u1eb7c bi\u1ec7t (l\u00e0m chung - l\u00e0m ri\u00eang), t\u00f9y t\u1eebng s\u1ed1 li\u1ec7u b\u00e0i to\u00e1n, ta c\u00f3 th\u1ec3 gi\u1eef nguy\u00ean \u0111\u01a1n v\u1ecb \u0111o th\u1eddi gian \u1edf ph\u00fat \u0111\u1ec3 l\u1eadp ph\u01b0\u01a1ng tr\u00ecnh.<\/span>"}]}],"id_ques":988},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["5"]]],"list":[{"point":10,"width":50,"type_input":"","ques":"M\u1ed9t \u0111\u1ed9i xe c\u1ea7n chuy\u00ean ch\u1edf $120$ t\u1ea5n h\u00e0ng. H\u00f4m l\u00e0m vi\u1ec7c c\u00f3 $2$ xe ph\u1ea3i r\u1eddi \u0111i l\u00e0m vi\u1ec7c kh\u00e1c. Do \u0111\u00f3 m\u1ed7i xe c\u00f2n l\u1ea1i ph\u1ea3i ch\u1edf th\u00eam $16$ t\u1ea5n h\u00e0ng. H\u1ecfi \u0111\u1ed9i xe c\u00f3 bao nhi\u00eau xe?<br\/><b> \u0110\u00e1p s\u1ed1:<\/b> _input_ (xe)","hint":"","explain":"<span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn:<\/span><br\/><b>B\u01b0\u1edbc 1:<\/b> G\u1ecdi s\u1ed1 xe c\u1ee7a \u0111\u1ed9i xe l\u00e0 \u1ea9n.<br\/><b>B\u01b0\u1edbc 2:<\/b> Bi\u1ec3u di\u1ec5n s\u1ed1 t\u1ea5n h\u00e0ng m\u1ed7i xe ph\u1ea3i ch\u1edf ban \u0111\u1ea7u v\u00e0 trong th\u1ef1c t\u1ebf.<br\/><b>B\u01b0\u1edbc 3:<\/b> L\u1eadp ph\u01b0\u01a1ng tr\u00ecnh v\u00e0 gi\u1ea3i ph\u01b0\u01a1ng tr\u00ecnh.<br\/><b>B\u01b0\u1edbc 4:<\/b> Lo\u1ea1i nghi\u1ec7m (n\u1ebfu c\u00f3) r\u1ed3i k\u1ebft lu\u1eadn.<br\/>L\u1eadp b\u1ea3ng:<br\/><table><tr><th><\/th><th>T\u1ed5ng s\u1ed1 h\u00e0ng<\/th><th>S\u1ed1 xe<\/th><th>S\u1ed1 t\u1ea5n\/xe<\/th><\/tr><tr><td>Ban \u0111\u1ea7u<\/td><td>$120$<\/td><td>$x$<\/td><td>$\\dfrac {120}{x}$<\/td><\/tr><tr><td>Khi l\u00e0m vi\u1ec7c<\/td><td>$120$<\/td><td>$x-2$<\/td><td>$\\dfrac {120}{x-2}$<\/td><\/tr><\/table><br\/><span class='basic_green'>B\u00e0i gi\u1ea3i<\/span><br\/>G\u1ecdi s\u1ed1 xe ban \u0111\u1ea7u c\u1ee7a \u0111\u1ed9i xe l\u00e0 $x$ (xe, $x>0$)<br\/>S\u1ed1 t\u1ea5n h\u00e0ng m\u1ed7i xe ph\u1ea3i ch\u1edf l\u00e0 $\\dfrac {120}{x}$ (t\u1ea5n)<br\/>S\u1ed1 xe th\u1ef1c t\u1ebf tham gia ch\u1edf h\u00e0ng l\u00e0 $x-2$ (xe)<br\/>S\u1ed1 t\u1ea5n h\u00e0ng th\u1ef1c t\u1ebf m\u1ed7i xe ph\u1ea3i ch\u1edf l\u00e0 $\\dfrac {120}{x-2}$(t\u1ea5n)<br\/>Do m\u1ed7i xe c\u00f2n l\u1ea1i ph\u1ea3i ch\u1edf th\u00eam $16$ t\u1ea5n h\u00e0ng n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh: <br\/>$\\dfrac {120}{x-2}-\\dfrac {120}{x}=16\\\\ \\Leftrightarrow 120(x-2)-120x=16x(x-2)\\\\ \\Leftrightarrow 16x^2-32x-240=0\\\\ \\Leftrightarrow x^2-2x-15=0\\\\ \\Leftrightarrow(x+3)(x-5)=0 \\\\ \\Leftrightarrow \\left[\\begin{aligned}&x=-3\\,\\,\\text{(lo\u1ea1i)}\\\\&x=5\\,\\,\\text{(th\u1ecfa m\u00e3n)}\\end{aligned}\\right.$<br\/>V\u1eady \u0111\u1ed9i xe c\u00f3 $5$ xe.<br\/><span class='basic_pink'>V\u1eady s\u1ed1 c\u1ea7n \u0111i\u1ec1n v\u00e0o ch\u1ed7 tr\u1ed1ng l\u00e0 $5$<\/span><\/span>"}]}],"id_ques":989},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["40"]]],"list":[{"point":10,"width":50,"type_input":"","ques":"<span class='basic_left'>M\u1ed9t m\u00e1y bay tr\u1ef1c th\u0103ng bay t\u1eeb $A$ \u0111\u1ebfn $B$ c\u00e1ch nhau $960 km$ v\u1edbi v\u1eadn t\u1ed1c $280 km\/h$. Khi bay t\u1eeb $A$ \u0111\u1ebfn $B$ do b\u1ecb gi\u00f3 c\u1ea3n n\u00ean th\u1eddi gian bay ph\u1ea3i nhi\u1ec1u h\u01a1n $1$ gi\u1edd so v\u1edbi th\u1eddi gian bay t\u1eeb $B$ \u0111\u1ebfn $A$ (do \u0111\u01b0\u1ee3c gi\u00f3 \u0111\u1ea9y). T\u00ednh v\u1eadn t\u1ed1c c\u1ee7a gi\u00f3.<br\/><b> \u0110\u00e1p s\u1ed1: <\/b> _input_ ($km\/h$)<\/span>","hint":"T\u01b0\u01a1ng t\u1ef1 b\u00e0i to\u00e1n thuy\u1ec1n \u0111i xu\u00f4i d\u00f2ng v\u00e0 ng\u01b0\u1ee3c d\u00f2ng.<br\/>Khi \u0111i t\u1eeb $A$ \u0111\u1ebfn $B$: V\u1eadn t\u1ed1c ng\u01b0\u1ee3c chi\u1ec1u $=$ v\u1eadn t\u1ed1c m\u00e1y bay $-$ v\u1eadn t\u1ed1c gi\u00f3.<br\/>Khi \u0111i t\u1eeb $B$ \u0111\u1ebfn $A$: v\u1eadn t\u1ed1c xu\u00f4i chi\u1ec1u $=$ v\u1eadn t\u1ed1c m\u00e1y bay $+$ v\u1eadn t\u1ed1c gi\u00f3.","explain":"<span class='basic_left'><span class='basic_green'>L\u1eadp b\u1ea3ng:<\/span><br\/><table><tr><th><\/th><th>Qu\u00e3ng \u0111\u01b0\u1eddng $AB$ ($km$)<\/th><th>V\u1eadn t\u1ed1c bay ($km\/h$)<\/th><th>Th\u1eddi gian (gi\u1edd)<\/th><\/tr><tr><td>Bay t\u1eeb $A$ \u0111\u1ebfn $B$<\/td><td>$960$<\/td><td>$280-x$<\/td><td>$\\dfrac {960}{280-x}$<\/td><\/tr><tr><td>Bay t\u1eeb $B$ \u0111\u1ebfn $A$<\/td><td>$960$<\/td><td>$280+x$<\/td><td>$\\dfrac {960}{280+x}$<\/td><\/tr><\/table><br\/><span class='basic_green'>B\u00e0i gi\u1ea3i<\/span><br\/>G\u1ecdi v\u1eadn t\u1ed1c gi\u00f3 l\u00e0 $x$ ($km,\\, x > 0$)<br\/>V\u1eadn t\u1ed1c c\u1ee7a m\u00e1y bay khi bay t\u1eeb $A$ \u0111\u1ebfn $B$ l\u00e0 $280-x$ ($km\/h$)<br\/>Th\u1eddi gian m\u00e1y bay bay t\u1eeb $A$ \u0111\u1ebfn $B$ l\u00e0 $\\dfrac {960}{280-x}$ (gi\u1edd)<br\/>V\u1eadn t\u1ed1c m\u00e1y bay bay t\u1eeb $B$ \u0111\u1ebfn $A$ l\u00e0 $280+x$($km\/h$)<br\/>Th\u1eddi gian m\u00e1y bay bay t\u1eeb $B$ \u0111\u1ebfn $A$ l\u00e0 $\\dfrac {960}{280+x}$ (gi\u1edd)<br\/>V\u00ec th\u1eddi gian m\u00e1y bay bay t\u1eeb $A$ \u0111\u1ebfn $B$ nhi\u1ec1u h\u01a1n $1$ gi\u1edd n\u00ean ta c\u00f3 ph\u01b0\u01a1ng tr\u00ecnh: <br\/>$\\dfrac {960}{280-x}-\\dfrac {960}{280+x}=1\\\\ \\Leftrightarrow 960(280+x)-960(280-x)=(280-x)(280+x)\\\\ \\Leftrightarrow x^2+1920x-78400=0\\\\ \\Leftrightarrow x^2-40x+1960x-78400=0\\\\ \\Leftrightarrow x(x-40)+1960(x-40)=0\\\\ \\Leftrightarrow (x-40)(x+1960)=0\\\\ \\Leftrightarrow\\left[\\begin{aligned} &x=40\\,\\,\\text {(th\u1ecfa m\u00e3n)}\\\\ &x=-1960\\,\\,\\text{(lo\u1ea1i)}\\\\ \\end{aligned} \\right. $<br\/>V\u1eady v\u1eadn t\u1ed1c c\u1ee7a gi\u00f3 l\u00e0 $40 km\/h$.<br\/><span class='basic_pink'>V\u1eady s\u1ed1 c\u1ea7n \u0111i\u1ec1n v\u00e0o ch\u1ed7 tr\u1ed1ng l\u00e0 $40$<\/span><\/span>"}]}],"id_ques":990}],"lesson":{"save":0,"level":3}}