{"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":5,"width":40,"type_input":"","ques":"<span class='basic_left'> Ng\u0169 gi\u00e1c c\u00f3 $\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}$ \u0111\u01b0\u1eddng ch\u00e9o. <\/span> ","explain":" <span class='basic_left'> Ng\u0169 gi\u00e1c l\u00e0 h\u00ecnh c\u00f3 5 c\u1ea1nh <br\/> S\u1ed1 \u0111\u01b0\u1eddng ch\u00e9o trong ng\u0169 gi\u00e1c l\u00e0: <br\/> $\\dfrac{5(5-3)}{2}=5$ (\u0111\u01b0\u1eddng ch\u00e9o) <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0: $5$ <\/span> <br\/> <b> L\u01b0u \u00fd: <\/b> <i> S\u1ed1 \u0111\u01b0\u1eddng ch\u00e9o trong \u0111a gi\u00e1c c\u00f3 $n$ c\u1ea1nh l\u00e0: $\\dfrac{n(n-3)}{2}$. <\/i> <\/span> "}]}],"id_ques":1561},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["0"]]],"list":[{"point":5,"width":40,"type_input":"","ques":"<span class='basic_left'> Tam gi\u00e1c c\u00f3 $\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}$ \u0111\u01b0\u1eddng ch\u00e9o. <\/span> ","explain":" <span class='basic_left'> Tam gi\u00e1c l\u00e0 h\u00ecnh c\u00f3 $3$ c\u1ea1nh. <br\/> S\u1ed1 \u0111\u01b0\u1eddng ch\u00e9o trong t\u1ee9 gi\u00e1c l\u00e0: <br\/> $\\dfrac{3(3-3)}{2}=0$ (\u0111\u01b0\u1eddng ch\u00e9o). <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $0$. <\/span> <br\/> <b> L\u01b0u \u00fd: <\/b> <i> S\u1ed1 \u0111\u01b0\u1eddng ch\u00e9o trong \u0111a gi\u00e1c c\u00f3 $n$ c\u1ea1nh l\u00e0: $\\dfrac{n(n-3)}{2}$. <\/i> <\/span> "}]}],"id_ques":1562},{"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":5,"width":40,"type_input":"","ques":"<span class='basic_left'> Ng\u0169 gi\u00e1c \u0111\u1ec1u c\u00f3 bao nhi\u00eau g\u00f3c b\u1eb1ng nhau? <br\/><br\/> <b> \u0110\u00e1p \u00e1n: <\/b> $\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}$ g\u00f3c <\/span> ","explain":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai11/lv1/img\/H821_D1_1.jpg' \/><\/center> Ng\u0169 gi\u00e1c \u0111\u1ec1u c\u00f3 $5 $g\u00f3c b\u1eb1ng nhau. <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $5$. <\/span> <\/span> "}]}],"id_ques":1563},{"time":24,"part":[{"title":"L\u1ef1a ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang nh\u1ea5t","title_trans":"","temp":"multiple_choice","correct":[[4]],"list":[{"point":5,"ques":" <span class='basic_left'> T\u1ee9 gi\u00e1c \u0111\u1ec1u l\u00e0: <\/span>","select":[" A. H\u00ecnh thang c\u00e2n"," B. H\u00ecnh ch\u1eef nh\u1eadt","C. H\u00ecnh thoi","D. H\u00ecnh vu\u00f4ng"],"explain":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai11/lv1/img\/H821_D1_2.jpg' \/><\/center> T\u1ee9 gi\u00e1c \u0111\u1ec1u l\u00e0 t\u1ee9 gi\u00e1c c\u00f3 $4$ c\u1ea1nh b\u1eb1ng nhau v\u00e0 $4$ g\u00f3c b\u1eb1ng nhau n\u00ean t\u1ee9 gi\u00e1c \u0111\u1ec1u l\u00e0 h\u00ecnh vu\u00f4ng.<br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 D. <\/span> <br\/> <b> L\u01b0u \u00fd: <\/b> <i> \u0110a gi\u00e1c \u0111\u1ec1u l\u00e0 \u0111a gi\u00e1c c\u00f3 c\u00e1c g\u00f3c b\u1eb1ng nhau v\u00e0 c\u00e1c c\u1ea1nh b\u1eb1ng nhau. <\/i> <\/span> ","column":2}]}],"id_ques":1564},{"time":24,"part":[{"title":"L\u1ef1a ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang nh\u1ea5t","title_trans":"","temp":"multiple_choice","correct":[[3]],"list":[{"point":5,"ques":" <span class='basic_left'> Di\u1ec7n t\u00edch h\u00ecnh vu\u00f4ng b\u1eb1ng: <\/span>","select":[" A. T\u00edch hai \u0111\u01b0\u1eddng ch\u00e9o"," B. L\u1eadp ph\u01b0\u01a1ng m\u1ed9t c\u1ea1nh","C. B\u00ecnh ph\u01b0\u01a1ng m\u1ed9t c\u1ea1nh","D. N\u1eeda t\u00edch hai \u0111\u01b0\u1eddng ch\u00e9o"],"explain":" <span class='basic_left'> Di\u1ec7n t\u00edch h\u00ecnh vu\u00f4ng b\u1eb1ng b\u00ecnh ph\u01b0\u01a1ng m\u1ed9t c\u1ea1nh c\u1ee7a n\u00f3. <br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 C. <\/span> <\/span> ","column":2}]}],"id_ques":1565},{"time":24,"part":[{"title":"L\u1ef1a ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang nh\u1ea5t","title_trans":"","temp":"multiple_choice","correct":[[1]],"list":[{"point":5,"ques":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai11/lv1/img\/H821_D1_3.jpg' \/><\/center> Di\u1ec7n t\u00edch tam gi\u00e1c $ABC$ trong h\u00ecnh tr\u00ean l\u00e0: <\/span>","select":[" A. $\\dfrac{1}{2}AB.AC$"," B. $\\dfrac{1}{2}(AB+BC+AC)$","C. $AB.AC$","D. $AB+BC+AC$"],"explain":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai11/lv1/img\/H821_D1_3.jpg' \/><\/center> Di\u1ec7n t\u00edch tam gi\u00e1c vu\u00f4ng b\u1eb1ng m\u1ed9t n\u1eeda t\u00edch hai c\u1ea1nh g\u00f3c vu\u00f4ng. <br\/> Do \u0111\u00f3: $S_{ABC}=\\dfrac{1}{2}AB.AC$ <br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 A. <\/span> <\/span> ","column":2}]}],"id_ques":1566},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["84"]]],"list":[{"point":5,"width":40,"type_input":"","ques":"<span class='basic_left'> H\u00ecnh ch\u1eef nh\u1eadt c\u00f3 \u0111\u1ed9 d\u00e0i c\u00e1c c\u1ea1nh l\u00e0 $7\\, cm$ v\u00e0 $12\\, cm$. Di\u1ec7n t\u00edch h\u00ecnh ch\u1eef nh\u1eadt \u0111\u00f3 l\u00e0 bao nhi\u00eau? <br\/><br\/> <b> \u0110\u00e1p \u00e1n: <\/b> $\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}$ $(cm^2)$ <\/span> ","explain":" <span class='basic_left'> Di\u1ec7n t\u00edch h\u00ecnh ch\u1eef nh\u1eadt \u0111\u00f3 l\u00e0: <br\/> $7.12=84\\,(cm^2)$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $84$. <\/span> <br\/> <b> L\u01b0u \u00fd: <\/b> <i> Di\u1ec7n t\u00edch h\u00ecnh ch\u1eef nh\u1eadt b\u1eb1ng t\u00edch hai c\u1ea1nh c\u1ee7a n\u00f3. <\/i> <\/span> "}]}],"id_ques":1567},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["10"]]],"list":[{"point":5,"width":40,"type_input":"","ques":"<span class='basic_left'> Tam gi\u00e1c vu\u00f4ng c\u00f3 hai c\u1ea1nh g\u00f3c vu\u00f4ng l\u1ea7n l\u01b0\u1ee3t d\u00e0i $5\\, cm$ v\u00e0 $4\\, cm$. Di\u1ec7n t\u00edch tam gi\u00e1c vu\u00f4ng \u0111\u00f3 l\u00e0 bao nhi\u00eau? <br\/><br\/> <b> \u0110\u00e1p \u00e1n: <\/b> $\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}$ $(cm^2)$ <\/span> ","explain":" <span class='basic_left'> Di\u1ec7n t\u00edch tam gi\u00e1c vu\u00f4ng \u0111\u00e3 cho l\u00e0: <br\/> $\\dfrac{1}{2}.5.4=10\\,(cm^2)$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $10$. <\/span> <br\/> <b> L\u01b0u \u00fd: <\/b> <i> Di\u1ec7n t\u00edch tam gi\u00e1c vu\u00f4ng b\u1eb1ng n\u1eeda t\u00edch hai c\u1ea1nh g\u00f3c vu\u00f4ng. <\/i> <\/span> "}]}],"id_ques":1568},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["12"]]],"list":[{"point":5,"width":40,"type_input":"","ques":"<span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai11/lv1/img\/H821_D1_4.jpg' \/><\/center> Tam gi\u00e1c $ABC$ c\u00e2n t\u1ea1i $A$, bi\u1ebft $AB=5\\,cm$ v\u00e0 \u0111\u01b0\u1eddng cao $AH=4\\,cm$ <br\/> Di\u1ec7n t\u00edch tam gi\u00e1c $ABC$ l\u00e0 bao nhi\u00eau? <br\/><br\/> <b> \u0110\u00e1p \u00e1n: <\/b> $ S_{ABC}=\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}$ $(cm^2)$ <\/span> ","hint":"T\u00ednh \u0111\u1ed9 d\u00e0i c\u1ea1nh $BC$ r\u1ed3i t\u00ednh di\u1ec7n t\u00edch $\\Delta ABC$.","explain":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai11/lv1/img\/H821_D1_4.jpg' \/><\/center> X\u00e9t $\\Delta ABH$ vu\u00f4ng t\u1ea1i $H$ (gi\u1ea3 thi\u1ebft). <br\/> $AB^2=AH^2+BH^2$ (\u0111\u1ecbnh l\u00ed Pi - ta - go) <br\/> $\\Rightarrow BH^2=AB^2-AH^2$ <br\/> $\\Rightarrow BH^2=5^2-4^2=9$ <br\/> $\\Rightarrow BH=3\\,(cm)$ <br\/> Do $\\Delta ABC$ c\u00e2n t\u1ea1i $A$ n\u00ean: $BC=2BH=6\\,cm$ <br\/> Di\u1ec7n t\u00edch tam gi\u00e1c $ABC$ l\u00e0: <br\/> $S_{ABC}=\\dfrac{1}{2}.AH.BC$ <br\/> $=\\dfrac{1}{2}.4.6=12\\,(cm^2)$. <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $12$. <\/span> <br\/> <b> L\u01b0u \u00fd: <\/b> <i> Di\u1ec7n t\u00edch tam gi\u00e1c th\u01b0\u1eddng th\u00ec b\u1eb1ng n\u1eeda t\u00edch \u0111\u01b0\u1eddng cao v\u1edbi c\u1ea1nh \u0111\u00e1y t\u01b0\u01a1ng \u1ee9ng. <\/i> <\/span> "}]}],"id_ques":1569},{"time":24,"part":[{"title":"L\u1ef1a ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang nh\u1ea5t","title_trans":"","temp":"multiple_choice","correct":[[2]],"list":[{"point":5,"ques":" <span class='basic_left'> Di\u1ec7n t\u00edch h\u00ecnh ch\u1eef nh\u1eadt thay \u0111\u1ed5i th\u1ebf n\u00e0o n\u1ebfu chi\u1ec1u d\u00e0i v\u00e0 chi\u1ec1u r\u1ed9ng \u0111\u1ec1u g\u1ea5p l\u00ean $3$ l\u1ea7n. <\/span>","select":[" A. Di\u1ec7n t\u00edch t\u0103ng l\u00ean $3$ l\u1ea7n"," B. Di\u1ec7n t\u00edch t\u0103ng l\u00ean $9$ l\u1ea7n","C. Di\u1ec7n t\u00edch t\u0103ng l\u00ean $6$ l\u1ea7n","D. \u0110\u00e1p \u00e1n kh\u00e1c"],"hint":"T\u00ednh di\u1ec7n t\u00edch h\u00ecnh ch\u1eef nh\u1eadt ban \u0111\u1ea7u v\u00e0 sau khi thay \u0111\u1ed5i chi\u1ec1u d\u00e0i v\u00e0 chi\u1ec1u r\u1ed9ng.","explain":" <span class='basic_left'> G\u1ecdi chi\u1ec1u d\u00e0i v\u00e0 chi\u1ec1u r\u1ed9ng h\u00ecnh ch\u1eef nh\u1eadt khi ch\u01b0a t\u0103ng l\u00e0: $a$ v\u00e0 $b$ $(a > b)$ <br\/> Di\u1ec7n t\u00edch ban \u0111\u1ea7u c\u1ee7a h\u00ecnh ch\u1eef nh\u1eadt l\u00e0: $a.b=ab$ <br\/> T\u0103ng chi\u1ec1u d\u00e0i l\u00ean $3$ l\u1ea7n th\u00ec chi\u1ec1u d\u00e0i m\u1edbi l\u00e0: $3a$ <br\/> T\u0103ng chi\u1ec1u r\u1ed9ng l\u00ean $3$ l\u1ea7n th\u00ec chi\u1ec1u r\u1ed9ng m\u1edbi l\u00e0: $3b$ <br\/> Di\u1ec7n t\u00edch h\u00ecnh ch\u1eef nh\u1eadt sau khi t\u0103ng chi\u1ec1u d\u00e0i v\u00e0 chi\u1ec1u r\u1ed9ng l\u00e0: $3a.3b=9ab$ <br\/> Do \u0111\u00f3: Di\u1ec7n t\u00edch h\u00ecnh ch\u1eef nh\u1eadt l\u00fac sau t\u0103ng $9$ l\u1ea7n so v\u1edbi ban \u0111\u1ea7u <br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 B. <\/span> <\/span> ","column":2}]}],"id_ques":1570},{"time":24,"part":[{"title":"L\u1ef1a ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang nh\u1ea5t","title_trans":"","temp":"multiple_choice","correct":[[4]],"list":[{"point":5,"ques":" <span class='basic_left'> Di\u1ec7n t\u00edch h\u00ecnh ch\u1eef nh\u1eadt thay \u0111\u1ed5i th\u1ebf n\u00e0o n\u1ebfu chi\u1ec1u d\u00e0i t\u0103ng l\u00ean $3$ l\u1ea7n v\u00e0 chi\u1ec1u r\u1ed9ng gi\u1ea3m \u0111i $3$ l\u1ea7n. <\/span>","select":[" A. Di\u1ec7n t\u00edch gi\u1ea3m \u0111i $3$ l\u1ea7n"," B. Di\u1ec7n t\u00edch t\u0103ng l\u00ean $3$ l\u1ea7n","C. Di\u1ec7n t\u00edch t\u0103ng l\u00ean $9$ l\u1ea7n","D. \u0110\u00e1p \u00e1n kh\u00e1c"],"hint":"T\u00ednh di\u1ec7n t\u00edch h\u00ecnh ch\u1eef nh\u1eadt ban \u0111\u1ea7u v\u00e0 sau khi thay \u0111\u1ed5i chi\u1ec1u d\u00e0i v\u00e0 chi\u1ec1u r\u1ed9ng.","explain":" <span class='basic_left'> G\u1ecdi chi\u1ec1u d\u00e0i v\u00e0 chi\u1ec1u r\u1ed9ng h\u00ecnh ch\u1eef nh\u1eadt l\u00fac \u0111\u1ea7u l\u00e0: $a$ v\u00e0 $b$ $(a > b)$ <br\/> Di\u1ec7n t\u00edch ban \u0111\u1ea7u c\u1ee7a h\u00ecnh ch\u1eef nh\u1eadt l\u00e0: $a.b=ab$ <br\/> T\u0103ng chi\u1ec1u d\u00e0i l\u00ean $3$ l\u1ea7n th\u00ec chi\u1ec1u d\u00e0i m\u1edbi l\u00e0: $3a$ <br\/> Gi\u1ea3m chi\u1ec1u r\u1ed9ng \u0111i $3$ l\u1ea7n th\u00ec chi\u1ec1u r\u1ed9ng m\u1edbi l\u00e0: $\\dfrac{b}{3}$ <br\/> Di\u1ec7n t\u00edch h\u00ecnh ch\u1eef nh\u1eadt sau khi thay \u0111\u1ed5i chi\u1ec1u d\u00e0i v\u00e0 chi\u1ec1u r\u1ed9ng l\u00e0: $3a.\\dfrac{b}{3}$$=ab$ <br\/> Do \u0111\u00f3: Di\u1ec7n t\u00edch h\u00ecnh ch\u1eef nh\u1eadt l\u00fac sau kh\u00f4ng \u0111\u1ed5i so v\u1edbi ban \u0111\u1ea7u. <br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 D. <\/span> <\/span> ","column":2}]}],"id_ques":1571},{"time":24,"part":[{"title":"L\u1ef1a ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang nh\u1ea5t","title_trans":"","temp":"multiple_choice","correct":[[1]],"list":[{"point":5,"ques":" <span class='basic_left'> Di\u1ec7n t\u00edch h\u00ecnh vu\u00f4ng thay \u0111\u1ed5i th\u1ebf n\u00e0o n\u1ebfu t\u0103ng \u0111\u1ed9 d\u00e0i c\u1ea1nh c\u1ee7a n\u00f3 l\u00ean $1,5$ l\u1ea7n. <\/span>","select":[" A. Di\u1ec7n t\u00edch t\u0103ng l\u00ean $\\dfrac{9}{4}$ l\u1ea7n"," B. Di\u1ec7n t\u00edch t\u0103ng l\u00ean $1,5$ l\u1ea7n","C. Di\u1ec7n t\u00edch t\u0103ng l\u00ean $3$ l\u1ea7n","D. Di\u1ec7n t\u00edch t\u0103ng l\u00ean $6$ l\u1ea7n"],"hint":"T\u00ednh di\u1ec7n t\u00edch h\u00ecnh vu\u00f4ng ban \u0111\u1ea7u v\u00e0 sau khi thay \u0111\u1ed5i \u0111\u1ed9 d\u00e0i c\u1ea1nh c\u1ee7a n\u00f3.","explain":" <span class='basic_left'> G\u1ecdi \u0111\u1ed9 d\u00e0i c\u1ea1nh c\u1ee7a h\u00ecnh vu\u00f4ng l\u00fac \u0111\u1ea7u l\u00e0: $a$ $(a>0)$ <br\/> Di\u1ec7n t\u00edch ban \u0111\u1ea7u c\u1ee7a h\u00ecnh vu\u00f4ng l\u00e0: $a^2$ <br\/> \u0110\u1ed9 d\u00e0i c\u1ea1nh t\u0103ng l\u00ean $1,5$ l\u1ea7n th\u00ec \u0111\u1ed9 d\u00e0i c\u1ea1nh c\u1ee7a h\u00ecnh vu\u00f4ng l\u00e0: $1,5a$ <br\/> Di\u1ec7n t\u00edch h\u00ecnh vu\u00f4ng sau khi thay \u0111\u1ed5i \u0111\u1ed9 d\u00e0i c\u1ea1nh l\u00e0: $(1,5a)^2=\\dfrac{9}{4}a^2$ <br\/> Do \u0111\u00f3: Di\u1ec7n t\u00edch h\u00ecnh vu\u00f4ng l\u00fac sau t\u0103ng g\u1ea5p $\\dfrac{9}{4}$ l\u1ea7n so v\u1edbi ban \u0111\u1ea7u. <br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 A. <\/span> <\/span> ","column":2}]}],"id_ques":1572},{"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":5,"width":40,"type_input":"","ques":"<span class='basic_left'> Cho $\\Delta ABC$ c\u00f3 di\u1ec7n t\u00edch l\u00e0 $20\\,cm^2$ v\u00e0 c\u1ea1nh $BC$ l\u00e0 $8 cm$. <br\/> T\u00ednh \u0111\u1ed9 d\u00e0i \u0111\u01b0\u1eddng cao \u1ee9ng v\u1edbi c\u1ea1nh $BC$ c\u1ee7a $\\Delta ABC$. <br\/><br\/> <b> \u0110\u00e1p \u00e1n: <\/b> \u0110\u1ed9 d\u00e0i \u0111\u01b0\u1eddng cao c\u1ea7n t\u00ecm l\u00e0 $\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}$ $(cm)$ <\/span> ","hint":" T\u00ednh \u0111\u01b0\u1eddng cao th\u00f4ng qua c\u00f4ng th\u1ee9c t\u00ednh di\u1ec7n t\u00edch $\\Delta ABC$.","explain":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai11/lv1/img\/H821_D2_2.jpg' \/><\/center> G\u1ecdi $AH$ l\u00e0 \u0111\u01b0\u1eddng cao \u1ee9ng v\u1edbi c\u1ea1nh $BC$ trong $\\Delta ABC$. <br\/> Ta c\u00f3: <br\/> $S_{ABC}=\\dfrac{1}{2}.AH.BC$ <br\/> $\\Rightarrow AH=2S_{ABC}:BC$ <br\/> $\\Rightarrow AH=(2.20):8 $ <br\/> $\\Rightarrow AH=5\\,(cm)$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $5$. <\/span> <br\/> <b> L\u01b0u \u00fd: <\/b> <i> Di\u1ec7n t\u00edch tam gi\u00e1c b\u1eb1ng n\u1eeda t\u00edch \u0111\u1ed9 d\u00e0i \u0111\u01b0\u1eddng cao v\u1edbi \u0111\u00e1y t\u01b0\u01a1ng \u1ee9ng. <\/i> <\/span> "}]}],"id_ques":1573},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["54"]]],"list":[{"point":5,"width":40,"type_input":"","ques":"<span class='basic_left'> Cho $\\Delta ABC$ c\u00f3 \u0111\u01b0\u1eddng cao $AH=9\\,cm; BC=12\\,cm$ <br\/> T\u00ednh di\u1ec7n t\u00edch $\\Delta ABC$. <br\/><br\/> <b> \u0110\u00e1p \u00e1n: <\/b> $S_{ABC}=\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}$ $(cm^2)$ <\/span> ","explain":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai11/lv1/img\/H821_D2_2.jpg' \/><\/center> Di\u1ec7n t\u00edch $\\Delta ABC$ l\u00e0: <br\/> $S_{ABC}=\\dfrac{1}{2}.AH.BC$ <br\/> $=\\dfrac{1}{2}.9.12$ <br\/> $=54\\,(cm^2)$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $54$. <\/span> <br\/> <b> L\u01b0u \u00fd: <\/b> <i> Di\u1ec7n t\u00edch tam gi\u00e1c b\u1eb1ng n\u1eeda t\u00edch \u0111\u1ed9 d\u00e0i \u0111\u01b0\u1eddng cao v\u1edbi \u0111\u00e1y t\u01b0\u01a1ng \u1ee9ng. <\/i> <\/span> "}]}],"id_ques":1574},{"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":5,"width":40,"type_input":"","ques":"<span class='basic_left'> Cho $\\Delta ABC$ vu\u00f4ng t\u1ea1i $A$. Bi\u1ebft $BC=5\\,cm; AC=3\\,cm$ <br\/> T\u00ednh di\u1ec7n t\u00edch $\\Delta ABC$ <br\/><br\/> <b> \u0110\u00e1p \u00e1n: <\/b> $S_{ABC}=\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}$ $(cm^2)$ <\/span> ","hint":"T\u00ednh c\u1ea1nh $AB$ r\u1ed3i t\u00ednh di\u1ec7n t\u00edch $\\Delta ABC$","explain":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai11/lv1/img\/H821_D1_5.jpg' \/><\/center> Do $\\Delta ABC$ vu\u00f4ng t\u1ea1i $A$ n\u00ean: <br\/> $AB^2+AC^2=BC^2$ (\u0111\u1ecbnh l\u00ed Pi - ta - go) <br\/> $\\Rightarrow AB^2=BC^2-AC^2$ <br\/> $\\Rightarrow AB^2=5^2-3^2=16$ <br\/> $\\Rightarrow AB=4\\,(cm)$ <br\/> Di\u1ec7n t\u00edch $\\Delta ABC$ l\u00e0: <br\/> $S_{ABC}=\\dfrac{1}{2}.AB.AC$ <br\/> $=\\dfrac{1}{2}.4.3$ <br\/> $=6\\,(cm^2)$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $6$. <\/span> <br\/> <b> L\u01b0u \u00fd: <\/b> <i> Di\u1ec7n t\u00edch tam gi\u00e1c vu\u00f4ng b\u1eb1ng n\u1eeda t\u00edch \u0111\u1ed9 d\u00e0i hai c\u1ea1nh g\u00f3c vu\u00f4ng. <\/i> <\/span> "}]}],"id_ques":1575},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["8"]]],"list":[{"point":5,"width":40,"type_input":"","ques":"<span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai11/lv1/img\/H821_D1_6.jpg' \/><\/center> Cho h\u00ecnh ch\u1eef nh\u1eadt $ABCD$ nh\u01b0 h\u00ecnh v\u1ebd tr\u00ean, bi\u1ebft $AB=12\\,cm; AD=8\\,cm$ <br\/> T\u00ednh di\u1ec7n t\u00edch h\u00ecnh ch\u1eef nh\u1eadt $EGHF$ <br\/><br\/> <b> \u0110\u00e1p \u00e1n: <\/b> $S_{EGHF}=\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}$ $(cm^2)$ <\/span> ","hint":"T\u00ednh c\u1ea1nh $EG$ v\u00e0 $EF$ r\u1ed3i t\u00ednh di\u1ec7n t\u00edch EGHF","explain":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai11/lv1/img\/H821_D1_6.jpg' \/><\/center> Theo h\u00ecnh v\u1ebd \u0111\u1ec1 b\u00e0i \u0111\u00e3 cho: <br\/> $EF=\\dfrac{1}{2}FI=\\dfrac{1}{2}AD$$=\\dfrac{8}{2}=4\\,(cm)$ <br\/> $FC=\\dfrac{1}{2}AB$$=\\dfrac{12}{2}=6\\,(cm)$ <br\/> M\u00e0 $EG=FH=\\dfrac{1}{3}FC$$=\\dfrac{6}{3}=2\\,(cm)$ <br\/> Di\u1ec7n t\u00edch h\u00ecnh ch\u1eef nh\u1eadt $EGHF$ l\u00e0: <br\/> $EG.EF=2.4=8\\,(cm^2)$. <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng \u0111\u1ec3 \u0111\u01b0\u1ee3c k\u1ebft qu\u1ea3 l\u00e0 $8$. <\/span> <br\/> <b> L\u01b0u \u00fd: <\/b> <i> Di\u1ec7n t\u00edch h\u00ecnh ch\u1eef nh\u1eadt b\u1eb1ng t\u00edch \u0111\u1ed9 d\u00e0i hai c\u1ea1nh c\u1ee7a n\u00f3. <\/i> <\/span> "}]}],"id_ques":1576},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["22"]]],"list":[{"point":5,"width":40,"type_input":"","ques":"<span class='basic_left'> M\u1ed9t h\u00ecnh ch\u1eef nh\u1eadt c\u00f3 di\u1ec7n t\u00edch l\u00e0 $24\\,cm^2$, chi\u1ec1u d\u00e0i l\u00e0 $8 cm$. <br\/> T\u00ednh chu vi h\u00ecnh ch\u1eef nh\u1eadt \u0111\u00f3. <br\/><br\/> <b> \u0110\u00e1p \u00e1n: <\/b> $\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{} \\,(cm)$ <\/span> ","explain":" <span class='basic_left'> Chi\u1ec1u r\u1ed9ng h\u00ecnh ch\u1eef nh\u1eadt \u0111\u00f3 l\u00e0: <br\/> $24:8=3\\,(cm)$ <br\/> Chu vi c\u1ee7a h\u00ecnh ch\u1eef nh\u1eadt \u0111\u00f3 l\u00e0: <br\/> $2(8+3)=22\\,(cm)$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $22$. <\/span> <br\/> <b> L\u01b0u \u00fd: <\/b> <i> Chu vi h\u00ecnh ch\u1eef nh\u1eadt b\u1eb1ng 2 l\u1ea7n t\u1ed5ng \u0111\u1ed9 d\u00e0i hai c\u1ea1nh c\u1ee7a n\u00f3. <\/i> <\/span> "}]}],"id_ques":1577},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["300"]]],"list":[{"point":5,"width":40,"type_input":"","ques":"<span class='basic_left'> Cho tam gi\u00e1c $ABC$ vu\u00f4ng t\u1ea1i $A$. Tr\u00ean \u0111\u00f3 v\u1ebd h\u00ecnh ch\u1eef nh\u1eadt $ABEC$, bi\u1ebft $S_{ABC}=150\\,cm^2$ <br\/> T\u00ednh di\u1ec7n t\u00edch h\u00ecnh ch\u1eef nh\u1eadt $ABEC$. <br\/><br\/> <b> \u0110\u00e1p \u00e1n: <\/b> $S_{ABEC}=\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{} \\,(cm^2)$ <\/span> ","explain":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai11/lv1/img\/H821_D1_7.jpg' \/><\/center> Theo b\u00e0i, ta lu\u00f4n c\u00f3: $S_{ABEC}=2S_{ABC}$ <br\/> M\u00e0 $S_{ABC}=150\\,(cm^2)$ <br\/> $\\Rightarrow S_{ABEC}=2.150=300\\,(cm^2)$. <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $300$. <\/span> <\/span> "}]}],"id_ques":1578},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["4"]]],"list":[{"point":5,"width":40,"type_input":"","ques":"<span class='basic_left'> \u0110a gi\u00e1c $n$ c\u1ea1nh m\u00e0 t\u1ea5t c\u1ea3 c\u00e1c g\u00f3c \u0111\u1ec1u l\u00e0 g\u00f3c vu\u00f4ng. T\u00ecm $n$.<br\/><br\/> <b> \u0110\u00e1p \u00e1n: <\/b> $n=\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}$ <\/span> ","explain":" <span class='basic_left'> T\u1ed5ng c\u00e1c g\u00f3c c\u1ee7a \u0111a gi\u00e1c n c\u1ea1nh: <br\/> $(n-2).180^o$ <br\/> Theo b\u00e0i, ta c\u00f3: <br\/> $(n-2).180^o=n.90^o$ <br\/> $\\Rightarrow 2n-4=n$ <br\/> $\\Rightarrow n=4$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $4$. <\/span> <\/span> "}]}],"id_ques":1579},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["900"]]],"list":[{"point":5,"width":40,"type_input":"","ques":"<span class='basic_left'> T\u1ed5ng s\u1ed1 \u0111o c\u00e1c g\u00f3c c\u1ee7a \u0111a gi\u00e1c \u0111\u1ec1u $7$ c\u1ea1nh l\u00e0 $\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{} ^o$ <\/span> ","explain":" <span class='basic_left'> T\u1ed5ng s\u1ed1 \u0111o c\u00e1c g\u00f3c c\u1ee7a \u0111a gi\u00e1c \u0111\u1ec1u $7$ c\u1ea1nh l\u00e0: <br\/> $(7-2).180^o=900^o$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $900$. <\/span> <br\/> <b> L\u01b0u \u00fd: <\/b> <i> T\u1ed5ng s\u1ed1 \u0111o c\u00e1c g\u00f3c c\u1ee7a \u0111a gi\u00e1c $n$ c\u1ea1nh l\u00e0: $(n-2).180^o$. <\/i> <\/span> "}]}],"id_ques":1580}],"lesson":{"save":0,"level":1}}