{"segment":[{"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'> H\u00ecnh thang $ABCD$ c\u00f3 $AB \/\/ CD$ v\u00e0 $\\widehat{A}-\\widehat{D}=40^o; \\widehat{B}=3\\widehat{C}$. S\u1ed1 \u0111o c\u00e1c g\u00f3c c\u1ee7a h\u00ecnh thang \u0111\u00f3 l\u00e0: <\/span>","select":["A. $\\widehat{A}=70^o;\\widehat{B}=45^o; \\widehat{C}=135^o; \\widehat{D}=110^o$ ","B. $\\widehat{A}=110^o;\\widehat{B}=45^o; \\widehat{C}=135^o; \\widehat{D}=70^o$ ","C. $\\widehat{A}=110^o;\\widehat{B}=135^o; \\widehat{C}=45^o; \\widehat{D}=70^o$ "],"hint":" T\u1ed5ng hai g\u00f3c k\u1ec1 m\u1ed9t c\u1ea1nh b\u00ean l\u00e0 $180^o$, k\u1ebft h\u1ee3p v\u1edbi \u0111\u1ec1 b\u00e0i \u0111\u1ec3 t\u00ecm ra s\u1ed1 \u0111o c\u1ee7a c\u00e1c g\u00f3c.","explain":" <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai2/lv3/img\/H812_K1_1.jpg' \/><\/center> <span class='basic_left'> Theo b\u00e0i, $\\widehat{A}-\\widehat{D}=40^o$ <br\/> M\u1eb7t kh\u00e1c: $\\widehat{A}+\\widehat{D}=180^o$ <br\/> $\\Rightarrow \\left\\{ \\begin{align} & \\widehat{A}=\\dfrac{{{180}^{o}}+{{40}^{o}}}{2}={{110}^{o}} \\\\ & \\widehat{D}=\\dfrac{{{180}^{o}}-{{40}^{o}}}{2}={{70}^{o}} \\\\ \\end{align} \\right.$ <br\/> T\u01b0\u01a1ng t\u1ef1, ta c\u00f3: <br\/> $\\begin{aligned} & \\left\\{ \\begin{aligned} & \\widehat{B}+\\widehat{C}={{180}^{o}} \\\\ & \\widehat{B}=3\\widehat{C} \\\\ \\end{aligned} \\right. \\\\ & \\Rightarrow \\left\\{ \\begin{aligned} & 4\\widehat{C}={{180}^{o}} \\\\ & \\widehat{B}=3\\widehat{C} \\\\ \\end{aligned} \\right. \\\\ & \\Rightarrow \\left\\{ \\begin{aligned} & \\widehat{C}={{45}^{o}} \\\\ & \\widehat{B}={{135}^{o}} \\\\ \\end{aligned} \\right. \\\\ \\end{aligned}$ <br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 C. <\/span><\/span> ","column":1}]}],"id_ques":1331},{"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'> H\u00ecnh thang c\u00e2n $MNPQ$ c\u00f3 \u0111\u00e1y nh\u1ecf $MN=a; PN \\bot NQ$ v\u00e0 $\\widehat{M}+\\widehat{N}=2(\\widehat{P}+\\widehat{Q})$. Chu vi c\u1ee7a h\u00ecnh thang l\u00e0: <\/span>","select":["A. $5a$ ","B. $2a$ ","C. $4a$ ","C. $3a$ "],"hint":" T\u00ednh c\u00e1c c\u1ea1nh ch\u01b0a bi\u1ebft c\u1ee7a h\u00ecnh thang theo $a$.","explain":"<center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai2/lv3/img\/H812_K1_2.jpg' \/><\/center> <span class='basic_left'> Theo b\u00e0i, ta c\u00f3: <br\/> $\\widehat{M}+\\widehat{N}=2(\\widehat{P}+\\widehat{Q})$ <br\/> $\\Rightarrow 2\\widehat{N}=2.2\\widehat{P}$ (do $MNPQ$ l\u00e0 h\u00ecnh thang c\u00e2n). <br\/> $\\Rightarrow\\widehat{N}=2\\widehat{P}$ <br\/> M\u00e0 $\\widehat{N}+\\widehat{P}=180^o \\Rightarrow \\widehat {N}=120^o; \\widehat{P}=60^o$ <br\/> $ QN \\bot PN \\Rightarrow \\widehat{MNQ}=30^o; \\widehat{NQP}=30^o$ <br\/> M\u00e0 ta c\u00f3: $MNPQ$ l\u00e0 h\u00ecnh thang c\u00e2n, n\u00ean $\\widehat{MQP}=\\widehat{NPQ}=60^o$$\\Rightarrow \\widehat{MQN}=30^o$ <br\/> Do \u0111\u00f3, $\\Delta MNQ$ c\u00f3 $\\widehat{MNQ}=\\widehat{MQN}=30^o$ n\u00ean l\u00e0 tam gi\u00e1c c\u00e2n t\u1ea1i $M$. <br\/> $\\Rightarrow MN =MQ=NP=a$ <br\/> $\\Delta QNP$ vu\u00f4ng t\u1ea1i $N$ c\u00f3 $NP=a; \\widehat{NQP}=30^o \\Rightarrow QP=2a$. <br\/> Chu vi h\u00ecnh thang $MNPQ$ l\u00e0: <br\/> $MN+NP+PQ+MQ=a+a+2a+a=5a$. <br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 A. <\/span><\/span> ","column":4}]}],"id_ques":1332},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["60"]]],"list":[{"point":10,"width":40,"type_input":"","ques":"<span class='basic_left'> M\u1ed9t h\u00ecnh thang c\u00e2n c\u00f3 chu vi l\u00e0 $32\\, cm$. T\u1ed5ng hai \u0111\u00e1y l\u00e0 $18\\, cm$, hi\u1ec7u hai \u0111\u00e1y l\u00e0 $4\\, cm$. Hi\u1ec7u hai g\u00f3c k\u1ec1 c\u1ea1nh b\u00ean c\u1ee7a h\u00ecnh thang c\u00e2n l\u00e0 $ \\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}^o$ ","hint":" T\u00ecm \u0111\u1ed9 d\u00e0i hai \u0111\u00e1y v\u00e0 \u0111\u1ed9 d\u00e0i c\u1ea1nh b\u00ean, t\u1eeb \u0111\u00f3 suy ra s\u1ed1 \u0111o c\u00e1c g\u00f3c h\u00ecnh thang.","explain":" <span class='basic_left'> G\u1ecdi \u0111\u1ed9 d\u00e0i hai \u0111\u00e1y l\u00e0 $a, b\\, (a, b > 0)$. <br\/> Theo b\u00e0i, ta c\u00f3: <br\/> $\\left\\{ \\begin{aligned} & a+b=18 \\\\ & a-b=4 \\\\ \\end{aligned} \\right.\\Rightarrow \\left\\{ \\begin{aligned} & a=11 \\\\ & b=7 \\\\ \\end{aligned} \\right.$ <br\/> V\u00ec h\u00ecnh thang c\u00e2n c\u00f3 \u0111\u1ed9 d\u00e0i hai c\u1ea1nh b\u00ean b\u1eb1ng nhau n\u00ean: <br\/>\u0110\u1ed9 d\u00e0i c\u1ea1nh b\u00ean h\u00ecnh thang c\u00e2n l\u00e0: <br\/> $(32-7-11):2=7$ <br\/> H\u00ecnh thang c\u00e2n c\u00f3 \u0111\u00e1y nh\u1ecf b\u1eb1ng c\u1ea1nh b\u00ean n\u00ean c\u00e1c g\u00f3c c\u1ee7a h\u00ecnh thang l\u00e0 $60^o$ v\u00e0 $120^o$. <br\/> Hi\u1ec7u hai g\u00f3c k\u1ec1 c\u1ea1nh b\u00ean c\u1ee7a h\u00ecnh thang c\u00e2n l\u00e0: $120^o-60^o=60^o$. <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $60$. <\/span><\/span> "}]}],"id_ques":1333},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["6"]]],"list":[{"point":10,"width":40,"type_input":"","ques":"<span class='basic_left'> H\u00ecnh thang vu\u00f4ng c\u00f3 hai c\u1ea1nh \u0111\u00e1y l\u1ea7n l\u01b0\u1ee3t l\u00e0 $4\\, cm;\\, 7\\, cm$, m\u1ed9t g\u00f3c nh\u1ecdn c\u00f3 s\u1ed1 \u0111o l\u00e0 $60^o$. C\u1ea1nh b\u00ean l\u1edbn nh\u1ea5t c\u1ee7a h\u00ecnh thang l\u00e0 _input_ $(cm)$ <\/span>","explain":" V\u1ebd h\u00ecnh <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai2/lv3/img\/H812_K1_3.jpg' \/><\/center> <span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn:<\/span><br\/> K\u1ebb $BH\\bot DC$ t\u1ea1i $H$ <br\/> T\u00ednh \u0111\u1ed9 d\u00e0i $HC$ r\u1ed3i suy ra $BC$.<br\/> <span class='basic_green'>B\u00e0i gi\u1ea3i:<\/span><br\/> H\u00ecnh thang vu\u00f4ng $ABCD$ c\u00f3 $AB=4\\, cm; DC=7\\, cm$;$\\widehat{A}=\\widehat{D}=90^o;\\widehat{C}=60^o$. <br\/> $BC$ l\u00e0 c\u1ea1nh b\u00ean l\u1edbn nh\u1ea5t <br\/> T\u1eeb $B,$ k\u1ebb $BH \\bot DC$ t\u1ea1i $H$<br\/> C\u00f3 $AD \/\/ BH$ (c\u00f9ng vu\u00f4ng g\u00f3c v\u1edbi $DC$). <br\/> $\\Rightarrow AB=DH$ (t\u00ednh ch\u1ea5t \u0111o\u1ea1n ch\u1eafn) <br\/> $\\Rightarrow HC=DC-AB=3\\, cm$ <br\/> X\u00e9t $\\Delta BHC$ c\u00f3: $\\widehat{C}=60^o \\Rightarrow \\widehat{B}=30^o$ <br\/> $\\Rightarrow BC=2HC=6\\, cm$. <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $6$. <\/span><\/span> "}]}],"id_ques":1334},{"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":[[["135"],["45"]]],"list":[{"point":10,"width":40,"type_input":"","ques":"<span class='basic_left'> H\u00ecnh thang $ABCD$ bi\u1ebft $\\widehat{A}=\\widehat{B}={{90}^{o}};\\,\\,AB=BC=\\dfrac{1}{2}AD$. <br\/><br\/> <b> C\u00e2u 1:<\/b> T\u00ednh $\\widehat{C}, \\widehat{D}$. <br\/><br\/> <b> \u0110\u00e1p \u00e1n: <\/b> <br\/> $\\widehat{C}=\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}^o$ <br\/> $\\widehat{D}=\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}^o$ <\/span>","hint":" K\u1ebb $CE\\bot AD$t\u1ea1i$E$<br\/> X\u00e9t $\\Delta CED$ l\u00e0 tam gi\u00e1c g\u00ec?","explain":" V\u1ebd h\u00ecnh <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai2/lv3/img\/H812_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> K\u1ebb $CE\\bot AD$ t\u1ea1i $E$ <br\/> <b> B\u01b0\u1edbc 2: <\/b> Ch\u1ee9ng minh $\\Delta CED$ vu\u00f4ng c\u00e2n, suy ra s\u1ed1 \u0111o g\u00f3c $D$. <br\/> <b> B\u01b0\u1edbc 3: <\/b> T\u00ednh s\u1ed1 \u0111o g\u00f3c $C$ t\u1eeb $\\widehat{C}+\\widehat{D}=180^o$ <br\/> <span class='basic_green'>B\u00e0i gi\u1ea3i:<\/span><br\/> K\u1ebb $CE\\bot AD$ t\u1ea1i$E$<br\/> Ta c\u00f3 $AB\\bot AD\\, (\\text{gi\u1ea3 thi\u1ebft})\\Rightarrow CE\/\/AB$ (t\u1eeb $\\bot$ t\u1edbi \/\/)<br\/> M\u00e0 $\\left. \\begin{align} & AB\\bot BC\\,(\\text{gi\u1ea3 thi\u1ebft}) \\\\ & AD\\bot AB\\,\\left( \\text{gi\u1ea3 thi\u1ebft} \\right) \\\\ \\end{align} \\right\\}\\Rightarrow BC\/\/AD$ (t\u1eeb $\\bot$ t\u1edbi \/\/) <br\/> Suy ra $CE= AB, BC= AE$ (t\u00ednh ch\u1ea5t \u0111o\u1ea1n ch\u1eafn).<br\/> M\u00e0 $AB=BC=\\dfrac{1}{2}AD$ $\\Rightarrow CE=AE=ED$<br\/> X\u00e9t $\\Delta CED$ c\u00f3 $\\widehat{CED}={{90}^{o}}$ ; $CE = ED$ (ch\u1ee9ng minh tr\u00ean) <br\/> $\\Rightarrow \\Delta CED$ vu\u00f4ng c\u00e2n (\u0111\u1ecbnh l\u00ed)<br\/> $\\Rightarrow \\widehat{ECD}=\\widehat{D}=\\dfrac{{{90}^{o}}}{2}={{45}^{o}}$<br\/> M\u00e0 $BC\/\/ AD$ $\\Rightarrow \\widehat{C}+\\widehat{D}={{180}^{o}}$ (trong c\u00f9ng ph\u00eda b\u00f9 nhau). <br\/> $\\Rightarrow \\widehat{C}={{180}^{o}}-{{45}^{o}}={{135}^{o}}$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $135$ v\u00e0 $45$. <\/span><\/span> "}]}],"id_ques":1335},{"time":24,"part":[{"title":"L\u1ef1a ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang nh\u1ea5t.<br\/> Kh\u1eb3ng \u0111\u1ecbnh d\u01b0\u1edbi \u0111\u00e2y \u0111\u00fang hay sai","title_trans":"\u0110\u1ec1 chung cho hai c\u00e2u","temp":"multiple_choice","correct":[[1]],"list":[{"point":10,"ques":" <span class='basic_left'> H\u00ecnh thang $ABCD$ bi\u1ebft $\\widehat{A}=\\widehat{B}={{90}^{o}};\\,\\,AB=BC=\\dfrac{1}{2}AD$ <br\/><br\/> <b> C\u00e2u 2:<\/b> Ta ch\u1ee9ng minh \u0111\u01b0\u1ee3c $AC \\bot CD$. <\/span> <\/span> ","select":["\u0110\u00fang","Sai"],"hint":" $\\Delta ACD$ l\u00e0 tam gi\u00e1c g\u00ec?","explain":"<span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai2/lv3/img\/H812_K1_4.jpg' \/><\/center> X\u00e9t $\\Delta ACD:\\,\\,CE\\bot AD\\,\\,(\\text{gi\u1ea3 thi\u1ebft});\\,AE=ED\\,$ (ch\u1ee9ng minh c\u00e2u 1) <br\/> $\\Rightarrow \\Delta ACD$ c\u00e2n t\u1ea1i $C$. (t\u00ednh ch\u1ea5t)<br\/> $\\Rightarrow \\widehat{CAE}=\\widehat{CDE}={{45}^{o}}(t\u00ednh ch\u1ea5t) $<br\/> $\\Rightarrow \\widehat{ACD}={{90}^{o}}\\Rightarrow AC\\bot CD$ <br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0: \u0110\u00fang.<\/span>","column":2}]}],"id_ques":1336},{"time":24,"part":[{"title":"L\u1ef1a ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang nh\u1ea5t.<br\/> Kh\u1eb3ng \u0111\u1ecbnh d\u01b0\u1edbi \u0111\u00e2y \u0111\u00fang hay sai","title_trans":"\u0110\u1ec1 chung cho hai c\u00e2u","temp":"multiple_choice","correct":[[1]],"list":[{"point":10,"ques":" <span class='basic_left'> Cho tam gi\u00e1c $ABC$ c\u00e2n t\u1ea1i $A$. Tr\u00ean c\u00e1c c\u1ea1nh $AB, AC$ l\u1ea5y c\u00e1c \u0111i\u1ec3m $M, N$ sao cho $BM = CN$. <br\/><br\/> <b> C\u00e2u 1:<\/b> Ta ch\u1ee9ng minh \u0111\u01b0\u1ee3c t\u1ee9 gi\u00e1c $BMNC$ l\u00e0 h\u00ecnh thang c\u00e2n. <\/span> <\/span> ","select":["\u0110\u00fang","Sai"],"explain":"<span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai2/lv3/img\/H812_K1_5.jpg' \/><\/center>Theo b\u00e0i $\\Delta ABC$ c\u00e2n t\u1ea1i $A$ n\u00ean: <br\/> $\\widehat{B}=\\widehat{C}=\\dfrac{180^o-\\widehat{A}}{2}$ (1) <br\/> $AB=AC; BM=CN$ <br\/> $\\Rightarrow AM=AN \\Rightarrow \\Delta AMN$ c\u00e2n t\u1ea1i $A$. <br\/> $\\Rightarrow \\widehat{M_1}=\\widehat{N_1}=\\dfrac{180^o-\\widehat{A}}{2}$ (2) <br\/> T\u1eeb (1) v\u00e0 (2), ta c\u00f3: $ \\widehat{B}=\\widehat{M_1}$ <br\/> M\u00e0 $\\widehat{B}$ v\u00e0 $\\widehat{M_1}$ \u1edf v\u1ecb tr\u00ed \u0111\u1ed3ng v\u1ecb n\u00ean $MN\/\/ BC$<br\/>Suy ra $MNBC$ l\u00e0 h\u00ecnh thang. (3) <br\/> T\u1eeb (1) v\u00e0 (3) suy ra $BMNC$ l\u00e0 h\u00ecnh thang c\u00e2n. <br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0: \u0110\u00fang.<\/span>","column":2}]}],"id_ques":1337},{"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":[[["70"],["70"],["110"],["110"]]],"list":[{"point":10,"width":40,"type_input":"","ques":"<span class='basic_left'> Cho tam gi\u00e1c $ABC$ c\u00e2n t\u1ea1i $A$. Tr\u00ean c\u00e1c c\u1ea1nh $AB, AC$ l\u1ea5y c\u00e1c \u0111i\u1ec3m $M, N$ sao cho $BM = CN$. <br\/><br\/> <b> C\u00e2u 2:<\/b> Cho $\\widehat{A}=40^o$. T\u00ednh $\\widehat{B}, \\widehat{C}, \\widehat{BMN}$ v\u00e0 $\\widehat{MNC}$. <br\/><br\/> <b> \u0110\u00e1p \u00e1n: <\/b> <br\/> $\\widehat{B}=\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}^o$ <br\/> $\\widehat{C}=\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}^o$ <br\/> $\\widehat{BMN}=\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}^o$ <br\/> $\\widehat{MNC}=\\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/bai2/lv3/img\/H812_K1_5b.jpg' \/><\/center> <span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn:<\/span><br\/> <b> B\u01b0\u1edbc 1: <\/b> X\u00e9t tam gi\u00e1c $ABC$ \u0111\u1ec3 t\u00ecm g\u00f3c $B$ v\u00e0 $C$. <br\/> <b> B\u01b0\u1edbc 2: <\/b> Trong h\u00ecnh thang c\u00e2n $BMNC$, bi\u1ebft $B$ t\u1eeb \u0111\u00f3 t\u00ednh ra g\u00f3c $BMN$ v\u00e0 $MNC$. <br\/> <span class='basic_green'>B\u00e0i gi\u1ea3i:<\/span><br\/> Ta c\u00f3: $\\Delta ABC$ c\u00e2n t\u1ea1i $A$ (gi\u1ea3 thi\u1ebft), c\u00f3 $\\widehat{A}=40^o$ <br\/> $\\Rightarrow \\widehat{B}=\\widehat{C}=\\dfrac{180^o-40^o}{2}=70^o$ <br\/> Trong h\u00ecnh thang c\u00e2n $BMNC$: $\\widehat{B}+\\widehat{M_2}=180^o$ <br\/> $\\Rightarrow \\widehat{M_2}=180^o-70^o=110^o$ <br\/> $\\Rightarrow \\widehat{MNC}=\\widehat{M_2}=110^o$. <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $70, 70, 110$ v\u00e0 $110$. <\/span><\/span> "}]}],"id_ques":1338},{"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":[[["60"]]],"list":[{"point":10,"width":40,"type_input":"","ques":"<span class='basic_left'> H\u00ecnh thang c\u00e2n $ABCD\\, (AB \/\/ CD)$ c\u00f3 $BD$ l\u00e0 tia ph\u00e2n gi\u00e1c c\u1ee7a g\u00f3c $D$, $DB \\bot BC$. Bi\u1ebft $AB =4\\, cm$. <br\/><br\/> <b> C\u00e2u 1:<\/b> T\u00ednh $\\widehat{C}$. <br\/><br\/> <b> \u0110\u00e1p \u00e1n: <\/b> $\\widehat{C}=\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}^o$ <\/span>","explain":" V\u1ebd h\u00ecnh <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai2/lv3/img\/H812_K1_6.png' \/><\/center> <span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn:<\/span><br\/> <b> B\u01b0\u1edbc 1: <\/b> T\u00ecm m\u1ed1i li\u00ean h\u1ec7 gi\u1eefa g\u00f3c $\\widehat{C}$ v\u00e0 g\u00f3c $\\widehat{D_2}$. <br\/> <b> B\u01b0\u1edbc 2:<\/b> T\u00ednh $\\widehat{D_2}$ r\u1ed3i suy ra g\u00f3c $\\widehat{C}$. <br\/> <span class='basic_green'>B\u00e0i gi\u1ea3i:<\/span><br\/> Do $ABCD$ l\u00e0 h\u00ecnh thang c\u00e2n v\u1edbi hai \u0111\u00e1y $AB$ v\u00e0 $CD$, t\u1ee9c l\u00e0: $AB\/\/CD$ <br\/>$\\Rightarrow \\widehat{B_1}=\\widehat{D_2}$ (so le trong) (1)<br\/> M\u00e0 $BD$ l\u00e0 tia ph\u00e2n gi\u00e1c c\u1ee7a g\u00f3c $ADC$ n\u00ean: $\\widehat{D_1}=\\widehat{D_2}$ (2)<br\/> T\u1eeb (1) v\u00e0 (2) $\\Rightarrow \\widehat{B_1}=\\widehat{D_1}$( c\u00f9ng b\u1eb1ng $\\widehat{D_2}$)<br\/> Suy ra tam gi\u00e1c $ABD$ c\u00e2n t\u1ea1i $A$. $\\Rightarrow AD=AB=4\\, cm$ <br\/> Do \u0111\u00f3: $AD=BC=4\\, cm$ <br\/> Ta l\u1ea1i c\u00f3: $\\widehat{D_2}=\\dfrac{\\widehat{D}}{2}$, m\u00e0 $\\widehat{D}=\\widehat{C}$ <br\/> $\\Rightarrow \\widehat{C}=2\\widehat{D_2}$ <br\/> X\u00e9t tam gi\u00e1c vu\u00f4ng $BDC$ c\u00f3: <br\/>$\\widehat{B}+\\widehat{D_2}+\\widehat{C}=180^o$<br\/> $\\Rightarrow 90^o+\\widehat{D_2}+2\\widehat{D_2}=180^o$<br\/>$\\Rightarrow \\widehat{D_2}=30^o$<br\/> $\\Rightarrow \\widehat{C}=2.30^o=60^o$. <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $60$. <\/span><\/span> "}]}],"id_ques":1339},{"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":[[["20"]]],"list":[{"point":10,"width":40,"type_input":"","ques":"<span class='basic_left'> H\u00ecnh thang c\u00e2n $ABCD\\, (AB \/\/ CD)$ c\u00f3 $BD$ l\u00e0 tia ph\u00e2n gi\u00e1c c\u1ee7a g\u00f3c $D$, $DB \\bot BC$. Bi\u1ebft $AB =4\\, cm$. <br\/><br\/> <b> C\u00e2u 2:<\/b> Chu vi h\u00ecnh thang $ABCD$ l\u00e0 _input_ $(cm)$ <\/span>","explain":" V\u1ebd h\u00ecnh <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai2/lv3/img\/H812_K1_6.png' \/><\/center> <span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn:<\/span><br\/> <b> B\u01b0\u1edbc 1: <\/b> X\u00e9t trong tam gi\u00e1c $BCD$ \u0111\u1ec3 t\u00ednh \u0111\u1ed9 d\u00e0i $DC$ theo c\u1ea1nh $BC$. <br\/> <b> B\u01b0\u1edbc 2:<\/b> T\u00ednh chu vi c\u1ee7a h\u00ecnh thang. <br\/> <span class='basic_green'>B\u00e0i gi\u1ea3i:<\/span><br\/> Theo c\u00e2u 1, ta \u0111\u00e3 t\u00ecm \u0111\u01b0\u1ee3c $\\widehat{D_2}=30^o$ v\u00e0 $\\widehat{C}=60^o$ <br\/> $\\Delta BDC$ c\u00f3 $\\widehat{D_2}=30^o$ <br\/> $\\Rightarrow BC=\\dfrac{DC}{2}$ <br\/> $\\Rightarrow DC =8\\, (cm)$ <br\/> Chu vi h\u00ecnh thang l\u00e0: <br\/> $ AD+AB+BC+DC$$=4+4+4+8=20\\, (cm)$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $20$. <\/span><\/span> "}]}],"id_ques":1340}],"lesson":{"save":0,"level":3}}