{"segment":[{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["5"]]],"list":[{"point":10,"width":40,"type_input":"","ques":"<span class='basic_left'> Cho h\u00ecnh thang c\u00e2n $ABCD\\, (AB \/\/ CD)$, $CD$ l\u00e0 \u0111\u00e1y l\u1edbn. G\u1ecdi $AH$ l\u00e0 \u0111\u01b0\u1eddng cao ($H\\in CD$) v\u00e0 $HC=5\\, cm$. \u0110\u1ed9 d\u00e0i \u0111\u01b0\u1eddng trung b\u00ecnh c\u1ee7a h\u00ecnh thang l\u00e0 _input_ $(cm)$ <\/span> ","hint":" K\u1ebb $BK\\bot CD$ t\u1ea1i $K$, t\u00ednh t\u1ed5ng $AB+CD$ theo $HC$. ","explain":"<center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai3/lv3/img\/H813_K1_1.jpg' \/><\/center> <span class='basic_left'> K\u1ebb $BK\\bot CD$ t\u1ea1i $K$ <br\/> Theo b\u00e0i: $AH\\bot CD $ t\u1ea1i $H$ $\\Rightarrow BK\/\/AH$ <br\/> M\u00e0 $AB\/\/HK \\Rightarrow AB=HK$ (t\u00ednh ch\u1ea5t \u0111o\u1ea1n ch\u1eafn) <br\/> Ta d\u1ec5 d\u00e0ng ch\u1ee9ng minh \u0111\u01b0\u1ee3c: $\\Delta ADH=\\Delta BCK$ (c\u1ea1nh huy\u1ec1n - g\u00f3c nh\u1ecdn)<br\/> $\\Rightarrow DH=CK$ (hai c\u1ea1nh t\u01b0\u01a1ng \u1ee9ng) <br\/> $\\Rightarrow AB+CD=HK+DH+HK+CK$ <br\/> $\\Rightarrow AB+CD=2(HK+CK)$$=2HC=2.5=10\\, (cm)$ <br\/> \u0110\u1ed9 \u0111\u00e0i \u0111\u01b0\u1eddng trung b\u00ecnh c\u1ee7a h\u00ecnh thang c\u00e2n $ABCD$ l\u00e0: <br\/> $\\dfrac{AB+CD}{2}=\\dfrac{10}{2}=5\\, (cm)$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $5$. <\/span><\/span> "}]}],"id_ques":1361},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["9"]]],"list":[{"point":10,"width":40,"type_input":"","ques":"<span class='basic_left'> M\u1ed9t h\u00ecnh thang c\u00e2n c\u00f3 c\u1ea1nh b\u00ean l\u00e0 $6\\, cm$. M\u1ed9t g\u00f3c \u1edf \u0111\u00e1y b\u1eb1ng $60^o$, \u0111\u00e1y l\u1edbn g\u1ea5p \u0111\u00f4i \u0111\u00e1y nh\u1ecf. \u0110\u01b0\u1eddng trung b\u00ecnh c\u1ee7a h\u00ecnh thang c\u00e2n \u0111\u00f3 l\u00e0 _input_ $(cm)$ <\/span> ","hint":" K\u1ebb t\u1eeb hai \u0111\u1ec9nh k\u1ec1 \u0111\u00e1y nh\u1ecf hai \u0111\u01b0\u1eddng th\u1eb3ng vu\u00f4ng g\u00f3c v\u1edbi \u0111\u00e1y l\u1edbn.","explain":"<center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai3/lv3/img\/H813_K1_2.jpg' \/><\/center> <span class='basic_left'> K\u1ebb $AH\\bot CD$ t\u1ea1i $H$; $BK\\bot CD$ t\u1ea1i $K$ <br\/> $\\Rightarrow AH\/\/BK$ <br\/> M\u00e0 $AB\/\/HK \\Rightarrow AB=HK$ (t\u00ednh ch\u1ea5t \u0111o\u1ea1n ch\u1eafn) <br\/>X\u00e9t $\\Delta ADH $ vu\u00f4ng t\u1ea1i $H$, c\u00f3 $AD= 6\\, cm; \\widehat{D}=60^o$ <br\/> $\\Rightarrow DH=\\dfrac{AD}{2}=3\\, (cm)$ <br\/> Ta d\u1ec5 d\u00e0ng ch\u1ee9ng minh \u0111\u01b0\u1ee3c: $\\Delta ADH=\\Delta BCK$ (c\u1ea1nh huy\u1ec1n - g\u00f3c nh\u1ecdn) <br\/> $\\Rightarrow DH=CK$ (hai c\u1ea1nh t\u01b0\u01a1ng \u1ee9ng) <br\/> M\u00e0 \u0111\u00e1y l\u1edbn g\u1ea5p \u0111\u00f4i \u0111\u00e1y nh\u1ecf n\u00ean: $HK=DH+CK=2DH=6\\, (cm)$ <br\/> $\\Rightarrow AB=HK=6\\, (cm) \\Rightarrow CD=2AB=12\\, (cm)$ <br\/> \u0110\u1ed9 d\u00e0i \u0111\u01b0\u1eddng trung b\u00ecnh c\u1ee7a h\u00ecnh thang c\u00e2n $ABCD$ l\u00e0: <br\/> $\\dfrac{AB+CD}{2}=\\dfrac{6+12}{2}=9\\, (cm)$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $9$. <\/span><\/span> "}]}],"id_ques":1362},{"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":" <span class='basic_left'> Cho h\u00ecnh thang c\u00e2n $ABCD \\,(AB \/\/ CD)$; $AC\\cap BD$ t\u1ea1i $O$. G\u1ecdi $M, N$ l\u1ea7n l\u01b0\u1ee3t l\u00e0 trung \u0111i\u1ec3m c\u1ee7a $AB$ v\u00e0 $CD$, $CD=2ON; AB+CD=5\\, (cm)$. \u0110\u1ed9 d\u00e0i $MN$ l\u00e0: <\/span>","select":["A. $2,5\\, cm$ ","B. $3\\, cm$ ","C. $4\\, cm$ ","D. $5\\, cm$ "],"hint":" X\u00e9t xem c\u00e1c tam gi\u00e1c $ABO$ v\u00e0 $COD$ l\u00e0 tam gi\u00e1c g\u00ec? <br\/> T\u00ednh $MN$ theo $AB+CD$.","explain":" <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai3/lv3/img\/H813_K1_3.jpg' \/><\/center> <span class='basic_left'> Theo b\u00e0i: $CD=2ON; DN=CN$ <br\/> $\\Rightarrow \\Delta COD$ vu\u00f4ng t\u1ea1i $O$. <br\/> $\\Rightarrow \\Delta AOB$ vu\u00f4ng t\u1ea1i $O$ <br\/> M\u00e0 $M$ l\u00e0 trung \u0111i\u1ec3m c\u1ee7a $AB$ $\\Rightarrow AB=2OM$ <br\/> $MN=OM+ON=\\dfrac{1}{2}(AB+CD)$$=\\dfrac{5}{2}=2,5\\, (cm)$ <br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 A. <\/span><\/span> ","column":4}]}],"id_ques":1363},{"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":" <span class='basic_left'> Cho $\\Delta ABC$ c\u00f3 chu vi l\u00e0 $36\\, cm$. G\u1ecdi $E, F, P$ l\u1ea7n l\u01b0\u1ee3t l\u00e0 trung \u0111i\u1ec3m c\u1ee7a c\u00e1c c\u1ea1nh $AB, BC$ v\u00e0 $CA$. Bi\u1ebft $AB:BC:CA=2:3:4$, chi\u1ec1u d\u00e0i c\u00e1c c\u1ea1nh c\u1ee7a $\\Delta EFP$ l\u00e0: <\/span>","select":["A. $4\\, cm;\\, 6\\, cm;\\, 8\\, cm$ ","B. $2\\, cm;\\, 3\\, cm;\\, 4\\, cm$ ","C. $3\\, cm;\\, 6\\, cm;\\, 12\\, cm$ ","D. $3\\, cm;\\, 6\\, cm;\\, 8\\, cm$ "],"explain":" <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai3/lv3/img\/H813_K1_4.jpg' \/><\/center> <span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn:<\/span><br\/><b> B\u01b0\u1edbc 1: <\/b>T\u00ecm \u0111\u1ed9 d\u00e0i c\u00e1c c\u1ea1nh $\\Delta ABC$. <br\/> <b> B\u01b0\u1edbc 2: <\/b> X\u00e1c \u0111\u1ecbnh m\u1ed1i quan h\u1ec7 gi\u1eefa $EF, PF, PE$ v\u1edbi c\u00e1c c\u1ea1nh c\u1ee7a $\\Delta ABC$ <br\/> <b> B\u01b0\u1edbc 3: <\/b> T\u00ednh \u0111\u1ed9 d\u00e0i c\u00e1c c\u1ea1nh c\u1ee7a $\\Delta EFP$ <br\/> <span class='basic_green'>B\u00e0i gi\u1ea3i:<\/span><br\/>Theo b\u00e0i $AB:BC:CA=2:3:4$ <br\/> $\\begin{aligned} & \\Rightarrow \\dfrac{AB}{2}=\\dfrac{BC}{3}=\\dfrac{AC}{4}=\\dfrac{AB+BC+AC}{2+3+4}=\\dfrac{36}{9}=4 \\\\ & \\Rightarrow \\left\\{ \\begin{aligned} & AB=8\\,\\,(cm) \\\\ & BC=12\\,\\,(cm) \\\\ & AC=16\\,\\,(cm) \\\\ \\end{aligned} \\right. \\\\ \\end{aligned}$<br\/> M\u00e0 $E, F, P$ l\u1ea7n l\u01b0\u1ee3t l\u00e0 trung \u0111i\u1ec3m c\u1ee7a c\u00e1c c\u1ea1nh $AB, BC$ v\u00e0 $CA$ n\u00ean: <br\/> $EF; FP$ v\u00e0 $PE$ l\u00e0 c\u00e1c \u0111\u01b0\u1eddng trung b\u00ecnh c\u1ee7a $\\Delta ABC$. <br\/> $\\Rightarrow EF=\\dfrac{1}{2}AC=8 \\, (cm); FP=\\dfrac{1}{2}AB=4\\, (cm); PE=\\dfrac{1}{2}BC=6\\, (cm)$ <br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 A. <\/span><\/span> ","column":2}]}],"id_ques":1364},{"time":24,"part":[{"title":"L\u1ef1a ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang nh\u1ea5t","title_trans":"","temp":"multiple_choice","correct":[[3]],"list":[{"point":10,"ques":" <span class='basic_left'> Cho h\u00ecnh thang $ABCD\\, (AB \/\/ CD; AB < CD)$. G\u1ecdi $M, N$ l\u1ea7n l\u01b0\u1ee3t l\u00e0 trung \u0111i\u1ec3m c\u1ee7a $AD$ v\u00e0 $BC$, $MN\\cap BD=E; MN\\cap AC=F$. Bi\u1ebft $MN=a; EF=b\\, (a > b)$. \u0110\u1ed9 d\u00e0i hai \u0111\u00e1y c\u1ee7a h\u00ecnh thang l\u00e0: <\/span>","select":["A. $AB=\\dfrac{a-b}{2}; CD=\\dfrac{a+b}{2}$ ","B. $AB=\\dfrac{a+b}{2}; CD=\\dfrac{a-b}{2}$ ","C. $AB=a-b; CD=a+b$ ","D. $AB=a+b; CD=a-b$ "],"hint":"Bi\u1ec3u di\u1ec5n t\u1ed5ng v\u00e0 hi\u1ec7u hai \u0111\u00e1y qua $a$ v\u00e0 $b$","explain":" <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai3/lv3/img\/H813_K1_5.jpg' \/><\/center> <span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn:<\/span><br\/><b> B\u01b0\u1edbc 1: <\/b>T\u00ecm t\u1ed5ng \u0111\u1ed9 d\u00e0i $AB+CD$ theo $a$. <br\/> <b> B\u01b0\u1edbc 2: <\/b> T\u00ecm hi\u1ec7u \u0111\u1ed9 d\u00e0i $CD-AB$ theo $b$. <br\/> <b> B\u01b0\u1edbc 3: <\/b> T\u00ecm \u0111\u1ed9 d\u00e0i $AB, CD$ khi bi\u1ebft t\u1ed5ng v\u00e0 hi\u1ec7u c\u1ee7a ch\u00fang. <br\/> <span class='basic_green'>B\u00e0i gi\u1ea3i:<\/span><br\/>Theo b\u00e0i $MN=a\\Rightarrow AB+CD=2a$ (1)<br\/> Do: $AM=MD; ME\/\/AB$ <br\/> $\\Rightarrow DE=EB$ <br\/> $\\Rightarrow ME$ l\u00e0 \u0111\u01b0\u1eddng trung b\u00ecnh c\u1ee7a $\\Delta ADB$ <br\/> $\\Rightarrow ME=\\dfrac{1}{2}AB$<br\/> T\u01b0\u01a1ng t\u1ef1: $MF=\\dfrac{1}{2}CD$ <br\/> $\\Rightarrow EF=MF-ME=\\dfrac{CD-AB}{2}$ <br\/> M\u00e0 $EF=b$ <br\/> $\\Rightarrow CD-AB=2EF=2b$ (2) <br\/> T\u1eeb (1) v\u00e0 (2) suy ra: $AB=a-b; CD=a+b$. <br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 C. <\/span><\/span> ","column":2}]}],"id_ques":1365},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"\u0110\u1ec1 chung cho ba c\u00e2u","temp":"fill_the_blank","correct":[[["120"]]],"list":[{"point":10,"width":40,"type_input":"","ques":"<span class='basic_left'> Cho h\u00ecnh thang c\u00e2n $ABCD\\, (AB \/\/ CD)$, \u0111\u00e1y l\u1edbn $CD=7\\, cm$, $\\widehat{C}=60^o; BC=4\\, cm$. <br\/><br\/> <b> C\u00e2u 1:<\/b> T\u00ednh $\\widehat{A}$. <br\/><br\/> <b> \u0110\u00e1p \u00e1n:<\/b> $\\widehat{A}= \\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}^o$<\/span>","explain":" <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai3/lv3/img\/H813_K1_6a.jpg' \/><\/center> <span class='basic_left'> Do $ABCD$ l\u00e0 h\u00ecnh thang c\u00e2n n\u00ean $\\widehat{B}=\\widehat{A}$ <br\/> M\u00e0 $\\widehat{C}+\\widehat{B}=180^o$ <br\/> $\\Rightarrow \\widehat{B}=180^o-60^o=120^o$ <br\/> $\\Rightarrow \\widehat{A}=120^o$. <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng \u0111\u1ec3 \u0111\u01b0\u1ee3c: $\\widehat{A}=120^o$. <\/span><\/span> "}]}],"id_ques":1366},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"\u0110\u1ec1 chung cho ba c\u00e2u","temp":"fill_the_blank","correct":[[["3"]]],"list":[{"point":10,"width":40,"type_input":"","ques":"<span class='basic_left'> Cho h\u00ecnh thang c\u00e2n $ABCD\\, (AB \/\/ CD)$, \u0111\u00e1y l\u1edbn $CD=7\\, cm$, $\\widehat{C}=60^o; BC=4\\, cm$. <br\/><br\/> <b> C\u00e2u 2:<\/b> T\u00ednh $AB$. <br\/><br\/> <b> \u0110\u00e1p \u00e1n:<\/b> $AB= \\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}$ (cm)<\/span>","hint":"Qua $B$ k\u1ebb $BE\/\/ AD\\,(E\\in DC)$<br\/> T\u00ednh $DE$ v\u00e0 $EC$ \u0111\u1ec3 t\u00ecm ra \u0111\u1ed9 d\u00e0i $AB$.","explain":" <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai3/lv3/img\/H813_K1_6.jpg' \/><\/center> <span class='basic_left'> Qua $B$ k\u1ebb $BE\/\/ AD; E\\in DC$ <br\/> $\\Rightarrow \\widehat{E_1}=\\widehat{D}$ (\u0111\u1ed3ng v\u1ecb) <br\/> M\u00e0 $\\widehat{D}=\\widehat{C}=60^o$ ($ABCD$ h\u00ecnh thang c\u00e2n) <br\/> $\\Rightarrow \\widehat{E_1}=60^o$ <br\/> Do \u0111\u00f3 $ \\Delta BEC$ l\u00e0 tam gi\u00e1c \u0111\u1ec1u. <br\/> $\\Rightarrow EC=BC= 4\\, cm$ <br\/> H\u01a1n n\u1eefa: $AB\/\/ DE$ (gi\u1ea3 thi\u1ebft); $AD \/\/ BE$ (c\u00e1ch d\u1ef1ng) <br\/> $\\Rightarrow AB=DE$ (t\u00ednh ch\u1ea5t \u0111o\u1ea1n ch\u1eafn) <br\/> M\u00e0 $DE=DC-EC=7-4=3\\, (cm)$ <br\/> Do v\u1eady: $AB=DE=3\\, (cm)$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $3$. <\/span><\/span> "}]}],"id_ques":1367},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"\u0110\u1ec1 chung cho ba c\u00e2u","temp":"fill_the_blank","correct":[[["5"]]],"list":[{"point":10,"width":40,"type_input":"","ques":"<span class='basic_left'> Cho h\u00ecnh thang c\u00e2n $ABCD\\, (AB \/\/ CD)$, \u0111\u00e1y l\u1edbn $CD=7\\, cm$, $\\widehat{C}=60^o; BC=4\\, cm$. <br\/><br\/> <b> C\u00e2u 3:<\/b> T\u00ednh \u0111\u1ed9 d\u00e0i \u0111\u01b0\u1eddng trung b\u00ecnh $MN$ c\u1ee7a h\u00ecnh thang c\u00e2n $ABCD$ $(M\\in AD; N\\in BC)$. <br\/><br\/> <b> \u0110\u00e1p \u00e1n:<\/b> $MN= \\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}$ cm<\/span>","explain":" <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai3/lv3/img\/H813_K1_6.jpg' \/><\/center> <span class='basic_left'> Theo c\u00e2u 2, ta t\u00ednh \u0111\u01b0\u1ee3c $AB=3\\, (cm)$ <br\/> \u0110\u1ed9 d\u00e0i \u0111\u01b0\u1eddng trung b\u00ecnh c\u1ee7a h\u00ecnh thang c\u00e2n $ABCD$ l\u00e0: <br\/> $MN=\\dfrac{AB+DC}{2}=\\dfrac{3+7}{2}=5\\, (cm)$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $5$. <\/span><\/span> "}]}],"id_ques":1368},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"\u0110\u1ec1 chung cho hai c\u00e2u","temp":"fill_the_blank","correct":[[["10"],["15"]]],"list":[{"point":10,"width":40,"type_input":"","ques":"<span class='basic_left'> Cho tam gi\u00e1c $ABC$, tr\u00ean c\u1ea1nh $AB$ l\u1ea5y hai \u0111i\u1ec3m $M, N$ sao cho $AM=MN=NB$. T\u1eeb $M$ v\u00e0 $N$ k\u1ebb c\u00e1c \u0111\u01b0\u1eddng th\u1eb3ng song song v\u1edbi $BC$ ch\u00fang c\u1eaft $AC$ l\u1ea7n l\u01b0\u1ee3t t\u1ea1i $M\u2019$ v\u00e0 $N\u2019$. <br\/> Bi\u1ebft $MM'=5\\,cm.$ <br\/><br\/> <b> C\u00e2u 1:<\/b> T\u00ednh \u0111\u1ed9 d\u00e0i c\u00e1c \u0111o\u1ea1n th\u1eb3ng $NN\u2019$ v\u00e0 $BC$. <br\/><br\/> <b> \u0110\u00e1p \u00e1n:<\/b> <br\/> $NN'= \\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}$ (cm) <br\/> $BC= \\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}$ (cm)<\/span>","hint":"$MM'$ l\u00e0 g\u00ec \u0111\u1ed1i v\u1edbi $\\Delta ANN'$. <br\/> X\u00e9t $NN'$ l\u00e0 g\u00ec \u0111\u1ed1i v\u1edbi h\u00ecnh thang $MM\u2019CB$. ","explain":"<center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai3/lv3/img\/H813_K1_7.jpg' \/><\/center> <span class='basic_left'> Trong $\\Delta ANN'$ c\u00f3: <br\/> + $AM=MN$ <br\/> + $MM'\/\/NN'$ <br\/> $\\Rightarrow MM'$ l\u00e0 \u0111\u01b0\u1eddng trung b\u00ecnh c\u1ee7a $\\Delta ANN'$ <br\/> $\\Rightarrow NN'=2MM'=2.5=10\\,(cm)$ <br\/> Theo b\u00e0i ta c\u00f3: $MM'\/\/BC$ <br\/> $\\Rightarrow MM'CB$ l\u00e0 h\u00ecnh thang. <br\/> Trong h\u00ecnh thang $MM\u2019CB$ ta c\u00f3 $MN=NB;NN'\/\/BC$ <br\/> $\\Rightarrow NN'$ l\u00e0 \u0111\u01b0\u1eddng trung b\u00ecnh c\u1ee7a h\u00ecnh thang $MM\u2019CB$. <br\/>Ta c\u00f3 $NN'=\\dfrac{MM'+BC}{2}$ <br\/> $\\Rightarrow BC=2NN'-MM'=2.10-5=15\\,(cm)$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $10$ v\u00e0 $15$. <\/span><\/span> "}]}],"id_ques":1369},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"\u0110\u1ec1 chung cho hai c\u00e2u","temp":"fill_the_blank","correct":[[["5"],["10"]]],"list":[{"point":10,"width":40,"type_input":"","ques":"<span class='basic_left'> Cho tam gi\u00e1c $ABC$, tr\u00ean c\u1ea1nh $AB$ l\u1ea5y hai \u0111i\u1ec3m $M, N$ sao cho $AM=MN=NB$ t\u1eeb $M$ v\u00e0 $N$ k\u1ebb c\u00e1c \u0111\u01b0\u1eddng th\u1eb3ng song song v\u1edbi $BC$ ch\u00fang c\u1eaft $AC$ l\u1ea7n l\u01b0\u1ee3t t\u1ea1i $M\u2019$ v\u00e0 $N\u2019$. <br\/> Bi\u1ebft $MM'=5\\,cm.$ <br\/><br\/> <b> C\u00e2u 2:<\/b> T\u1eeb $M$ k\u1ebb $MD \/\/ AC$ ($D\\in BC$) c\u1eaft $NN'$ t\u1ea1i $E$. T\u00ednh \u0111\u1ed9 d\u00e0i c\u00e1c \u0111o\u1ea1n th\u1eb3ng $EN$ v\u00e0 $BD$. <br\/><br\/> <b> \u0110\u00e1p \u00e1n:<\/b> <br\/> $EN= \\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}$ $(cm)$ <br\/> $BD= \\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}$ $(cm)$<\/span>","hint":" So s\u00e1nh $MM'$ v\u00e0 $DC$, $MM'$ v\u00e0 $N'E$. ","explain":"<center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai3/lv3/img\/H813_K1_7.jpg' \/><\/center> <span class='basic_left'> Ta c\u00f3: $MM' \/\/ CD; M'C \/\/ MD$ <br\/> $\\Rightarrow MM'=DC=5\\, (cm)$ (t\u00ednh ch\u1ea5t \u0111o\u1ea1n ch\u1eafn) <br\/> T\u01b0\u01a1ng t\u1ef1: $MM' =N'E=5\\, (cm)$ <br\/> Ta c\u00f3: $NN'=N'E+EN$ <br\/> $\\Rightarrow EN=10-5=5\\, (cm)$ <br\/> $DB=CB-CD=15-5=10\\, (cm)$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $5$ v\u00e0 $10$. <\/span><\/span> "}]}],"id_ques":1370}],"lesson":{"save":0,"level":3}}