{"segment":[{"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'> Cho h\u00ecnh v\u1ebd sau: <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai13/lv1/img\/H823_D1_1.jpg' \/><\/center> Bi\u1ebft $ABCD$ l\u00e0 h\u00ecnh ch\u1eef nh\u1eadt. T\u00ednh di\u1ec7n t\u00edch $ABCD$. <br\/> <b> \u0110\u00e1p \u00e1n: <\/b> $S_{ABCD}=\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}\\,(cm^2)$ <\/span> ","hint":" T\u00ecm \u0111\u1ed9 d\u00e0i c\u1ee7a $AB$ r\u1ed3i t\u00ednh di\u1ec7n t\u00edch h\u00ecnh ch\u1eef nh\u1eadt $ABCD$.","explain":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai13/lv1/img\/H823_D1_1.jpg' \/><\/center> X\u00e9t $\\Delta ABD$ vu\u00f4ng t\u1ea1i $A$: <br\/> $AB^2+AD^2=BD^2$ (\u0111\u1ecbnh l\u00ed Pi - ta - go) <br\/> $\\Rightarrow AB^2=BD^2-AD^2$ <br\/> $\\Rightarrow AB^2=5^2-3^2=16$ <br\/> $\\Rightarrow AB=4\\,(cm)$ <br\/> Di\u1ec7n t\u00edch h\u00ecnh ch\u1eef nh\u1eadt $ABCD$ l\u00e0: <br\/> $AB.AD=4.3=12\\,(cm^2)$ <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 h\u00ecnh ch\u1eef nh\u1eadt b\u1eb1ng t\u00edch hai c\u1ea1nh c\u1ee7a n\u00f3. <\/i> <\/span> "}]}],"id_ques":1621},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["14"]]],"list":[{"point":5,"width":40,"type_input":"","ques":"<span class='basic_left'> Cho h\u00ecnh v\u1ebd sau <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai13/lv1/img\/H823_D1_2.jpg' \/><\/center> Bi\u1ebft $\\Delta ABC$ c\u00e2n t\u1ea1i $C$. T\u00ednh di\u1ec7n t\u00edch $\\Delta ABC$. <br\/> <b> \u0110\u00e1p \u00e1n: <\/b> $S_{\\Delta ABC}=\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}\\,(cm^2)$ <\/span> ","explain":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai13/lv1/img\/H823_D1_2.jpg' \/><\/center> X\u00e9t $\\Delta ABC$ c\u00e2n t\u1ea1i $C$: <br\/> $BC=AC$ (t\u00ednh ch\u1ea5t) <br\/> $\\Rightarrow AC=7\\,cm$ <br\/> Di\u1ec7n t\u00edch tam gi\u00e1c $ABC$ l\u00e0: <br\/> $\\dfrac{1}{2}.BH.AC$ <br\/> $=\\dfrac{1}{2}.4.7=14\\,(cm^2)$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $14$. <\/span> <br\/> <b> L\u01b0u \u00fd: <\/b> <i> Di\u1ec7n t\u00edch tam gi\u00e1c b\u1eb1ng n\u1eeda t\u00edch \u0111\u01b0\u1eddng cao v\u1edbi \u0111\u00e1y t\u01b0\u01a1ng \u1ee9ng. <\/i> <\/span> "}]}],"id_ques":1622},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["48"]]],"list":[{"point":5,"width":40,"type_input":"","ques":"<span class='basic_left'> Cho h\u00ecnh v\u1ebd sau: <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai13/lv1/img\/H823_D1_3.jpg' \/><\/center> Bi\u1ebft $ABCD$ l\u00e0 h\u00ecnh thoi v\u00e0 $AO=4\\,cm; DO=6\\,cm$. <br\/> T\u00ednh di\u1ec7n t\u00edch $ABCD$. <br\/> <b> \u0110\u00e1p \u00e1n: <\/b> $S_{ABCD}=\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}\\,(cm^2)$ <\/span> ","explain":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai13/lv1/img\/H823_D1_3.jpg' \/><\/center> Theo t\u00ednh ch\u1ea5t h\u00ecnh thoi:<br\/> $AC=2AO=8\\,cm$ <br\/> $BD=2DO=12\\,(cm)$ <br\/> Di\u1ec7n t\u00edch h\u00ecnh thoi $ABCD$ l\u00e0: <br\/> $\\dfrac{1}{2}.AC.BD$ <br\/> $=\\dfrac{1}{2}.8.12=48\\,(cm^2)$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $48$. <\/span> <br\/> <b> L\u01b0u \u00fd: <\/b> <i> Di\u1ec7n t\u00edch h\u00ecnh thoi n\u1eeda t\u00edch hai \u0111\u01b0\u1eddng ch\u00e9o c\u1ee7a n\u00f3. <\/i> <\/span> "}]}],"id_ques":1623},{"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'> N\u1ebfu t\u0103ng m\u1ed7i c\u1ea1nh c\u1ee7a h\u00ecnh ch\u1eef nh\u1eadt l\u00ean $7$ l\u1ea7n th\u00ec di\u1ec7n t\u00edch h\u00ecnh ch\u1eef nh\u1eadt s\u1ebd: <\/span>","select":["A. T\u0103ng l\u00ean $49$ l\u1ea7n","B. T\u0103ng l\u00ean $14$ l\u1ea7n","C. T\u0103ng l\u00ean $21$ l\u1ea7n","D. T\u0103ng l\u00ean $7$ l\u1ea7n"],"explain":" <span class='basic_left'> G\u1ecdi \u0111\u1ed9 d\u00e0i hai c\u1ea1nh l\u00fac \u0111\u1ea7u c\u1ee7a h\u00ecnh ch\u1eef nh\u1eadt l\u00e0 $a$ v\u00e0 $b$ ($a > b > 0$). <br\/> Di\u1ec7n t\u00edch l\u00fac \u0111\u1ea7u c\u1ee7a h\u00ecnh ch\u1eef nh\u1eadt l\u00e0: <br\/> $S_{\\text{\u0111}}=ab$ <br\/> \u0110\u1ed9 d\u00e0i hai c\u1ea1nh sau khi t\u0103ng c\u1ee7a h\u00ecnh ch\u1eef nh\u1eadt l\u00e0: $7a$ v\u00e0 $7b$ <br\/> Di\u1ec7n t\u00edch l\u00fac sau c\u1ee7a h\u00ecnh ch\u1eef nh\u1eadt l\u00e0: <br\/> $S_s=7a.7b=49ab=49S_{\\text{\u0111}}$ <br\/> Di\u1ec7n t\u00edch h\u00ecnh ch\u1eef nh\u1eadt l\u00fac sau t\u0103ng l\u00ean $49$ l\u1ea7n so v\u1edbi di\u1ec7n t\u00edch ban \u0111\u1ea7u. <br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 A. <\/span> <\/span> ","column":2}]}],"id_ques":1624},{"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'> N\u1ebfu t\u0103ng chi\u1ec1u cao c\u1ee7a tam gi\u00e1c l\u00ean $10$ l\u1ea7n v\u00e0 gi\u1eef nguy\u00ean c\u1ea1nh \u0111\u00e1y t\u01b0\u01a1ng \u1ee9ng v\u1edbi \u0111\u01b0\u1eddng cao th\u00ec di\u1ec7n t\u00edch tam gi\u00e1c thay \u0111\u1ed5i nh\u01b0 th\u1ebf n\u00e0o? <\/span>","select":["A. T\u0103ng l\u00ean $100$ l\u1ea7n","B. T\u0103ng l\u00ean $10$ l\u1ea7n","C. T\u0103ng l\u00ean $20$ l\u1ea7n","D. Kh\u00f4ng \u0111\u1ed5i"],"explain":" <span class='basic_left'> G\u1ecdi \u0111\u1ed9 d\u00e0i \u0111\u01b0\u1eddng cao v\u00e0 c\u1ea1nh \u0111\u00e1y t\u01b0\u01a1ng \u1ee9ng trong tam gi\u00e1c l\u00e0 $h$ v\u00e0 $a$ ($a ; h > 0$). <br\/> Di\u1ec7n t\u00edch l\u00fac \u0111\u1ea7u c\u1ee7a tam gi\u00e1c l\u00e0: <br\/> $S_{\\text{\u0111}}=\\dfrac{1}{2}.h.a$ <br\/> Do di\u1ec7n t\u00edch tam gi\u00e1c t\u1ec9 l\u1ec7 thu\u1eadn v\u1edbi \u0111\u01b0\u1eddng cao. <br\/> N\u00ean khi t\u0103ng chi\u1ec1u cao c\u1ee7a tam gi\u00e1c l\u00ean $10$ l\u1ea7n v\u00e0 gi\u1eef nguy\u00ean c\u1ea1nh \u0111\u00e1y t\u01b0\u01a1ng \u1ee9ng. <br\/> Th\u00ec di\u1ec7n t\u00edch tam gi\u00e1c l\u00fac sau t\u0103ng l\u00ean $10$ l\u1ea7n so v\u1edbi di\u1ec7n t\u00edch ban \u0111\u1ea7u. <br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 B. <\/span> <\/span> ","column":2}]}],"id_ques":1625},{"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'> N\u1ebfu c\u00f9ng gi\u1ea3m hai \u0111\u01b0\u1eddng ch\u00e9o c\u1ee7a h\u00ecnh thoi \u0111i $6$ l\u1ea7n th\u00ec di\u1ec7n t\u00edch h\u00ecnh thoi s\u1ebd: <\/span>","select":["A. T\u0103ng l\u00ean $36$ l\u1ea7n","B. T\u0103ng l\u00ean $6$ l\u1ea7n","C. Gi\u1ea3m \u0111i $36$ l\u1ea7n","D. Kh\u00f4ng \u0111\u1ed5i"],"explain":" <span class='basic_left'> G\u1ecdi \u0111\u1ed9 d\u00e0i hai \u0111\u01b0\u1eddng ch\u00e9o c\u1ee7a h\u00ecnh thoi l\u00e0 $d_1$ v\u00e0 $d_2$ ($d_1 ; d_2 > 0$). <br\/> Di\u1ec7n t\u00edch l\u00fac \u0111\u1ea7u c\u1ee7a h\u00ecnh thoi l\u00e0: <br\/> $S_{\\text{\u0111}}=\\dfrac{1}{2}d_1d_2$ <br\/> \u0110\u1ed9 d\u00e0i hai \u0111\u01b0\u1eddng ch\u00e9o c\u1ee7a h\u00ecnh thoi sau khi c\u00f9ng gi\u1ea3m \u0111i $6$ l\u1ea7n l\u00e0: $\\dfrac{1}{6}d_1$ v\u00e0 $\\dfrac{1}{6}d_2$ <br\/> Di\u1ec7n t\u00edch l\u00fac sau c\u1ee7a h\u00ecnh thoi l\u00e0: <br\/> $S_s=\\dfrac{1}{2}.\\dfrac{1}{6}d_1.\\dfrac{1}{6}d_2$ <br\/> $=\\dfrac{1}{36}.\\dfrac{1}{2}d_1d_2=\\dfrac{1}{36}S_{\\text{\u0111}}$ <br\/> Di\u1ec7n t\u00edch h\u00ecnh thoi l\u00fac sau gi\u1ea3m \u0111i $36$ l\u1ea7n so v\u1edbi di\u1ec7n t\u00edch ban \u0111\u1ea7u. <br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 C. <\/span> <\/span> ","column":2}]}],"id_ques":1626},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["98"]]],"list":[{"point":5,"width":40,"type_input":"","ques":"<span class='basic_left'> H\u00ecnh ch\u1eef nh\u1eadt c\u00f3 chi\u1ec1u r\u1ed9ng l\u00e0 $7 \\,cm$, chi\u1ec1u d\u00e0i g\u1ea5p \u0111\u00f4i chi\u1ec1u r\u1ed9ng. Di\u1ec7n t\u00edch h\u00ecnh ch\u1eef nh\u1eadt l\u00e0 $\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}\\,(cm^2)$ <\/span> ","explain":" <span class='basic_left'> Chi\u1ec1u d\u00e0i h\u00ecnh ch\u1eef nh\u1eadt l\u00e0: <br\/> $7.2=14\\,(cm)$ <br\/> Di\u1ec7n t\u00edch h\u00ecnh ch\u1eef nh\u1eadt l\u00e0: <br\/> $7.14=98\\,(cm^2)$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $98$. <\/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":1627},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["42"]]],"list":[{"point":5,"width":40,"type_input":"","ques":"<span class='basic_left'> H\u00ecnh thang c\u00f3 \u0111\u1ed9 d\u00e0i hai c\u1ea1nh \u0111\u00e1y l\u00e0 $5 \\,cm$ v\u00e0 $9 \\,cm$. \u0110\u01b0\u1eddng cao h\u00ecnh thang h\u01a1n \u0111\u00e1y nh\u1ecf $1 \\,cm$. Di\u1ec7n t\u00edch h\u00ecnh thang l\u00e0 $\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}\\,(cm^2)$ <\/span> ","explain":" <span class='basic_left'> \u0110\u01b0\u1eddng cao c\u1ee7a h\u00ecnh thang l\u00e0: $5+1=6\\,(cm)$ <br\/> Di\u1ec7n t\u00edch h\u00ecnh thang \u0111\u00f3 l\u00e0: <br\/> $\\dfrac{6.(5+9)}{2}=42\\,(cm^2)$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $42$. <\/span> <br\/> <b> L\u01b0u \u00fd: <\/b> <i> Di\u1ec7n t\u00edch h\u00ecnh thang b\u1eb1ng n\u1eeda t\u00edch \u0111\u01b0\u1eddng cao v\u1edbi t\u1ed5ng hai \u0111\u00e1y. <\/i> <\/span> "}]}],"id_ques":1628},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["25"]]],"list":[{"point":5,"width":40,"type_input":"","ques":"<span class='basic_left'> M\u1ed9t tam gi\u00e1c c\u00f3 c\u1ea1nh \u0111\u00e1y l\u00e0 $10 \\,cm$. C\u1ea1nh \u0111\u00e1y g\u1ea5p \u0111\u00f4i \u0111\u01b0\u1eddng cao t\u01b0\u01a1ng \u1ee9ng. <br\/> Di\u1ec7n t\u00edch tam gi\u00e1c \u0111\u00f3 l\u00e0 $\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}\\,(cm^2)$ <\/span> ","explain":" <span class='basic_left'> \u0110\u1ed9 d\u00e0i \u0111\u01b0\u1eddng cao c\u1ee7a tam gi\u00e1c l\u00e0: <br\/>$10:2=5\\,(cm)$ <br\/> Di\u1ec7n t\u00edch tam gi\u00e1c \u0111\u00f3 l\u00e0: <br\/> $\\dfrac{1}{2}.5.10=25\\,(cm^2)$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $25$. <\/span> <br\/> <b> L\u01b0u \u00fd: <\/b> <i> Di\u1ec7n t\u00edch tam gi\u00e1c b\u1eb1ng n\u1eeda t\u00edch \u0111\u01b0\u1eddng cao v\u1edbi \u0111\u00e1y t\u01b0\u01a1ng \u1ee9ng. <\/i> <\/span> "}]}],"id_ques":1629},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["11"]]],"list":[{"point":5,"width":40,"type_input":"","ques":"<span class='basic_left'> Cho h\u00ecnh ch\u1eef nh\u1eadt $ABCD$ nh\u01b0 h\u00ecnh v\u1ebd sau: <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai13/lv1/img\/H823_D1_4.jpg' \/><\/center> Bi\u1ebft di\u1ec7n t\u00edch $ABCD$ l\u00e0 $143\\,cm^2$. T\u00ednh \u0111\u1ed9 d\u00e0i c\u1ea1nh $AD$. <br\/> <br\/> <b> \u0110\u00e1p \u00e1n: <\/b> $AD=\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}\\,(cm)$ <\/span> ","explain":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai13/lv1/img\/H823_D1_4.jpg' \/><\/center> Ta c\u00f3: $S_{ABCD}=AD.AB$ <br\/> $\\Rightarrow AD=S_{ABCD}:AB$ <br\/> \u0110\u1ed9 d\u00e0i c\u1ea1nh $AD$ l\u00e0: <br\/> $143:13=11\\,(cm)$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $11$. <\/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":1630},{"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 h\u00ecnh thang $ABCD$ nh\u01b0 h\u00ecnh v\u1ebd sau: <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai13/lv1/img\/H823_D1_5.jpg' \/><\/center> Bi\u1ebft di\u1ec7n t\u00edch $ABCD$ l\u00e0 $39\\,cm^2$ <br\/> T\u00ednh \u0111\u1ed9 d\u00e0i c\u1ea1nh $AH$. <br\/> <b> \u0110\u00e1p \u00e1n: <\/b> $AH=\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}\\,(cm)$ <\/span> ","explain":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai13/lv1/img\/H823_D1_5.jpg' \/><\/center> Ta c\u00f3: $S_{ABCD}=\\dfrac{1}{2}.AH.(AB+CD)$ <br\/> $\\Rightarrow AH=2S_{ABCD}:(AB+CD)$ <br\/> \u0110\u1ed9 d\u00e0i c\u1ea1nh $AH$ l\u00e0: <br\/> $(2.39):(5+8)=6\\,(cm)$ <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 h\u00ecnh thang b\u1eb1ng n\u1eeda t\u00edch \u0111\u01b0\u1eddng cao v\u1edbi t\u1ed5ng hai \u0111\u00e1y. <\/i> <\/span> "}]}],"id_ques":1631},{"time":24,"part":[{"title":"\u0110i\u1ec1n k\u1ebft qu\u1ea3 v\u00e0o \u00f4 tr\u1ed1ng","title_trans":"","temp":"fill_the_blank","correct":[[["11"]]],"list":[{"point":5,"width":40,"type_input":"","ques":"<span class='basic_left'> Cho h\u00ecnh thang $ABCD$ nh\u01b0 h\u00ecnh v\u1ebd sau: <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai13/lv1/img\/H823_D1_6.jpg' \/><\/center> Bi\u1ebft $AH=DC$; $S_{ABCD}=121\\,cm^2$. <br\/> T\u00ednh \u0111\u1ed9 d\u00e0i c\u1ea1nh $AB$. <br\/> <b> \u0110\u00e1p \u00e1n: <\/b> $AB=\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}\\,(cm)$ <\/span> ","hint":"T\u1eeb di\u1ec7n t\u00edch h\u00ecnh b\u00ecnh h\u00e0nh \u0111\u00e3 cho suy ra \u0111\u1ed9 d\u00e0i $DC$.","explain":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai13/lv1/img\/H823_D1_6.jpg' \/><\/center> Ta c\u00f3: $S_{ABCD}=AH.DC$ <br\/> M\u00e0 $AH=DC$ n\u00ean $S_{ABCD}=DC^2$ <br\/> $\\Rightarrow DC^2=121$ <br\/> $\\Rightarrow DC=11\\,(cm)$ <br\/> Theo t\u00ednh ch\u1ea5t h\u00ecnh b\u00ecnh h\u00e0nh th\u00ec $DC=AB$ <br\/> $\\Rightarrow AB=11\\,(cm)$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u00e0 $11$. <\/span> <br\/> <b> L\u01b0u \u00fd: <\/b> <i> Di\u1ec7n t\u00edch h\u00ecnh b\u00ecnh h\u00e0nh b\u1eb1ng t\u00edch \u0111\u01b0\u1eddng cao v\u1edbi \u0111\u00e1y t\u01b0\u01a1ng \u1ee9ng. <\/i> <\/span> "}]}],"id_ques":1632},{"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'> \u0110a gi\u00e1c l\u1ed3i $8$ c\u1ea1nh c\u00f3 s\u1ed1 \u0111\u01b0\u1eddng ch\u00e9o l\u00e0: <\/span>","select":["A. $40$","B. $32$","C. $20$","D. $16$"],"explain":" <span class='basic_left'> S\u1ed1 \u0111\u01b0\u1eddng ch\u00e9o c\u1ee7a \u0111a gi\u00e1c l\u1ed3i $8$ c\u1ea1nh l\u00e0: <br\/> $\\dfrac{8(8-3)}{2}=20$ (\u0111\u01b0\u1eddng) <br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 C. <\/span> <br\/> <b> L\u01b0u \u00fd: <\/b> <i> S\u1ed1 \u0111\u01b0\u1eddng ch\u00e9o c\u1ee7a \u0111a gi\u00e1c l\u1ed3i $n$ c\u1ea1nh l\u00e0: $\\dfrac{n(n-3)}{2}.$ <\/i> <\/span> ","column":4}]}],"id_ques":1633},{"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'> T\u1ed5ng s\u1ed1 \u0111o c\u00e1c g\u00f3c c\u1ee7a ng\u0169 gi\u00e1c l\u00e0: <\/span>","select":["A. $540^o$","B. $720^o$","C. $360^o$","D. $180^o$ "],"explain":" <span class='basic_left'> T\u1ed5ng s\u1ed1 \u0111o c\u00e1c g\u00f3c c\u1ee7a ng\u0169 gi\u00e1c l\u00e0: <br\/> $(5-2).180^o=540^o$ <br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 A. <\/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> ","column":4}]}],"id_ques":1634},{"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'> S\u1ed1 \u0111o m\u1ed7i g\u00f3c trong l\u1ee5c gi\u00e1c \u0111\u1ec1u l\u00e0: <\/span>","select":["A. $150^o$","B. $140^o$","C. $130^o$","D. $120^o$ "],"explain":" <span class='basic_left'> T\u1ed5ng s\u1ed1 \u0111o c\u00e1c g\u00f3c c\u1ee7a l\u1ee5c gi\u00e1c \u0111\u1ec1u l\u00e0: <br\/> $(6-2).180^o=720^o$ <br\/> S\u1ed1 \u0111o m\u1ed7i g\u00f3c trong l\u1ee5c gi\u00e1c \u0111\u1ec1u l\u00e0: <br\/> $720^o:6=120^o$ <br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 D. <\/span> <br\/> <b> L\u01b0u \u00fd: <\/b> <i> S\u1ed1 \u0111o m\u1ed7i g\u00f3c trong \u0111a gi\u00e1c \u0111\u1ec1u $n$ c\u1ea1nh l\u00e0: $\\dfrac{(n-2).180^o}{n}$ <\/i> <\/span> ","column":4}]}],"id_ques":1635},{"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'> \u0110a gi\u00e1c \u0111\u1ec1u c\u00f3 t\u1ed5ng s\u1ed1 \u0111o c\u00e1c g\u00f3c trong l\u00e0 $1440^o$. S\u1ed1 c\u1ea1nh c\u1ee7a \u0111a gi\u00e1c n\u00e0y l\u00e0: <\/span>","select":["A. $10$","B. $9$","C. $8$","D. $7$ "],"explain":" <span class='basic_left'> T\u1ed5ng s\u1ed1 \u0111o c\u00e1c g\u00f3c c\u1ee7a \u0111a gi\u00e1c \u0111\u1ec1u $n$ c\u1ea1nh l\u00e0: <br\/> $(n-2).180^o=1440^o$ <br\/> $\\Rightarrow n-2=8$ <br\/> $\\Rightarrow n=10$ <br\/> V\u1eady \u0111a gi\u00e1c \u0111\u1ec1u \u0111\u00f3 c\u00f3 $10$ c\u1ea1nh <br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 A. <\/span> <br\/> <b> L\u01b0u \u00fd: <\/b> <i> T\u1ed5ng s\u1ed1 \u0111o c\u00e1c g\u00f3c c\u1ee7a \u0111a gi\u00e1c \u0111\u1ec1u $n$ c\u1ea1nh l\u00e0: $(n-2).180^o$ <\/i> <\/span> ","column":4}]}],"id_ques":1636},{"time":24,"part":[{"title":"L\u1ef1a ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang nh\u1ea5t ","title_trans":"\u0110\u1ec1 chung cho hai c\u00e2u","temp":"multiple_choice","correct":[[1]],"list":[{"point":5,"ques":" <span class='basic_left'> Cho tam gi\u00e1c nh\u1ecdn $ABC\\, (AC > AB)$, \u0111\u01b0\u1eddng cao $AH$. G\u1ecdi $D, E, F$ theo th\u1ee9 t\u1ef1 l\u00e0 trung \u0111i\u1ec3m c\u1ee7a $AB, AC, BC$. <br\/> <b> C\u00e2u 1: <\/b> T\u1ee9 gi\u00e1c $DEFH$ l\u00e0 h\u00ecnh g\u00ec? <\/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/bai13/lv1/img\/H823_D1_7.jpg' \/><\/center> X\u00e9t $\\Delta ABC$ c\u00f3: $AD=DB,\\,\\,AE=EC$ <br\/> $\\Rightarrow DE\/\/BF;\\,\\,DE=\\dfrac{1}{2}BC=BF$ (t\u00ednh ch\u1ea5t \u0111\u01b0\u1eddng trung b\u00ecnh) <br\/>$\\Rightarrow BDEF$ l\u00e0 h\u00ecnh b\u00ecnh h\u00e0nh (d\u1ea5u hi\u1ec7u nh\u1eadn bi\u1ebft). <br\/> $\\Rightarrow \\widehat{EDH}=\\widehat{DHB}$ (so le trong) <br\/> X\u00e9t $\\Delta ABH$ vu\u00f4ng t\u1ea1i $H$, ta c\u00f3: <br\/> $AD=DB\\Rightarrow AD = BD=DH$ (t\u00ednh ch\u1ea5t trung tuy\u1ebfn trong tam gi\u00e1c vu\u00f4ng). <br\/> $\\Rightarrow \\Delta BDH$ c\u00e2n <br\/> $\\Rightarrow \\widehat{ABC}=\\widehat{DHB}$ <br\/> M\u00e0: $\\widehat{ABC}=\\widehat{DEF}$ (t\u00ednh ch\u1ea5t h\u00ecnh b\u00ecnh h\u00e0nh) <br\/> $\\Rightarrow \\widehat{EDH}=\\widehat{D\\text{EF}}$ (1) <br\/> M\u1eb7t kh\u00e1c $DE \/\/ HF$ (2) <br\/> T\u1eeb (1) v\u00e0 (2) suy ra t\u1ee9 gi\u00e1c $DEFH$ l\u00e0 h\u00ecnh thang c\u00e2n. <br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 A. <\/span> <\/span> ","column":4}]}],"id_ques":1637},{"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"],["12"]]],"list":[{"point":5,"width":40,"type_input":"","ques":"<span class='basic_left'> Cho tam gi\u00e1c nh\u1ecdn $ABC\\, (AC > AB)$, \u0111\u01b0\u1eddng cao $AH$. G\u1ecdi $D, E, F$ theo th\u1ee9 t\u1ef1 l\u00e0 trung \u0111i\u1ec3m c\u1ee7a $AB, AC, BC$.<br\/> <b> C\u00e2u 2: <\/b> Cho $AH=8\\,cm;\\, BC=10\\,cm$ v\u00e0 $BH = 4 \\, cm$. T\u00ednh di\u1ec7n t\u00edch c\u00e1c t\u1ee9 gi\u00e1c $BDEF$ v\u00e0 $DEFH$. <br\/> <b> \u0110\u00e1p \u00e1n: <\/b> <br\/> $S_{BDEF}=\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{}\\,(cm^2)$ <br\/> $S_{DEFH}=\\FormInput[40][bl_elm_true basic_elm basic_blank basic_blank_part]{} \\,(cm^2)$ <\/span> ","hint":"${{S}_{DEFH}}={{S}_{BDEF}}-{{S}_{BDH}}$.","explain":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai13/lv1/img\/H823_D1_7.jpg' \/><\/center> Theo c\u00e2u 1, ta \u0111\u00e3 ch\u1ee9ng minh \u0111\u01b0\u1ee3c $BDEF$ l\u00e0 h\u00ecnh b\u00ecnh h\u00e0nh v\u00e0 $DEFH$ l\u00e0 h\u00ecnh thang c\u00e2n. <br\/> K\u1ebb $EK\\bot BC$ t\u1ea1i $K$. <br\/> D\u1ec5 d\u00e0ng ch\u1ee9ng minh \u0111\u01b0\u1ee3c $EK=\\dfrac{1}{2}AH$ <br\/> ${{S}_{ABC}}=\\dfrac{1}{2}AH.BC$ <br\/> $=\\dfrac{1}{2}.8.10=40\\,\\,\\left( c{{m}^{2}} \\right)$ <br\/> ${{S}_{ABH}}=\\dfrac{1}{2}AH.BH$ <br\/> $=\\dfrac{1}{2}.8.4=16\\,\\,\\left( c{{m}^{2}} \\right)$ <br\/> ${{S}_{BDEF}}=BF.EK$$=\\dfrac{1}{2}BC.\\dfrac{1}{2}AH=\\dfrac{1}{4}.BC.AH=\\dfrac{1}{4}.10.8=20\\,\\left( c{{m}^{2}} \\right)$ <br\/> Ta l\u1ea1i c\u00f3: $BD=\\dfrac{1}{2}AB$ (gi\u1ea3 thi\u1ebft) <br\/> $\\Rightarrow S_{BDH}=\\dfrac{1}{2}S_{ABH}$ (Hai tam gi\u00e1c $BDH$ v\u00e0 $ABH$ c\u00f3 c\u00f9ng \u0111\u01b0\u1eddng cao h\u1ea1 t\u1eeb $H$ \u0111\u1ebfn $BD$ v\u00e0 $AB$) <br\/> V\u1eady ${{S}_{DEFH}}={{S}_{BDEF}}-{{S}_{BDH}}$ <br\/> $={{S}_{BDEF}}-\\dfrac{1}{2}{{S}_{ABH}}$ <br\/> $=20-\\dfrac{1}{2}.16=20-8=12\\,\\,\\left( c{{m}^{2}} \\right)$ <br\/> <span class='basic_pink'> V\u1eady c\u1ea7n \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng l\u1ea7n l\u01b0\u1ee3t l\u00e0 $20$ v\u00e0 $12$. <\/span> <\/span> "}]}],"id_ques":1638},{"time":24,"part":[{"title":"L\u1ef1a ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang nh\u1ea5t ","title_trans":"\u0110\u1ec1 chung cho hai c\u00e2u","temp":"multiple_choice","correct":[[4]],"list":[{"point":5,"ques":" <span class='basic_left'> Cho h\u00ecnh vu\u00f4ng $ABCD$ c\u00f3 c\u1ea1nh $12\\, cm$, $O$ l\u00e0 giao \u0111i\u1ec3m c\u1ee7a $AC$ v\u00e0 $BD$. G\u1ecdi $G, H, I, K$ l\u1ea7n l\u01b0\u1ee3t l\u00e0 trung \u0111i\u1ec3m c\u1ee7a $OA, OB, OC$ v\u00e0 $OD$. <br\/> <b> C\u00e2u 1: <\/b> T\u1ee9 gi\u00e1c $GHIK$ l\u00e0 h\u00ecnh g\u00ec? <\/span>","select":["A. H\u00ecnh b\u00ecnh h\u00e0nh","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/bai13/lv1/img\/H823_D1_8.jpg' \/><\/center> X\u00e9t $\\Delta OAB$ ta c\u00f3: $OG=GA;\\,\\,OH=HB$ <br\/> $\\Rightarrow GH=\\dfrac{1}{2}AB;\\,\\,GH\/\/AB$ <br\/> T\u01b0\u01a1ng t\u1ef1 $GK=\\dfrac{1}{2}AD;\\,\\,KI=\\dfrac{1}{2}DC;\\,\\,HI=\\dfrac{1}{2}BC$ <br\/> M\u00e0 $AB = BC = CD =DA\\Rightarrow GH=HI=IK=GK$. <br\/> M\u1eb7t kh\u00e1c: $GI\\bot HK$ t\u1ea1i $O$. <br\/> $\\Rightarrow $ T\u1ee9 gi\u00e1c $GHIK$ l\u00e0 h\u00ecnh vu\u00f4ng (d\u1ea5u hi\u1ec7u nh\u1eadn bi\u1ebft). <br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 D. <\/span> <\/span> ","column":4}]}],"id_ques":1639},{"time":24,"part":[{"title":"L\u1ef1a ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang nh\u1ea5t ","title_trans":"\u0110\u1ec1 chung cho hai c\u00e2u","temp":"multiple_choice","correct":[[2]],"list":[{"point":5,"ques":" <span class='basic_left'> Cho h\u00ecnh vu\u00f4ng $ABCD$ c\u00f3 c\u1ea1nh $12\\, cm$, $O$ l\u00e0 giao \u0111i\u1ec3m c\u1ee7a $AC$ v\u00e0 $BD$. G\u1ecdi $G, H, I, K$ l\u1ea7n l\u01b0\u1ee3t l\u00e0 trung \u0111i\u1ec3m c\u1ee7a $OA, OB, OC$ v\u00e0 $OD$. <br\/> <b> C\u00e2u 2: <\/b> Di\u1ec7n t\u00edch ph\u1ea7n h\u00ecnh vu\u00f4ng $ABCD$ n\u1eb1m ngo\u00e0i t\u1ee9 gi\u00e1c $GHIK$ l\u00e0: <\/span>","select":["A. $54\\,cm^2$","B. $108\\,cm^2$","C. $216\\,cm^2$ "],"hint":"T\u00ednh ${{S}_{GHIK}}$.","explain":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop8/toan/hinhhoc/bai13/lv1/img\/H823_D1_8.jpg' \/><\/center> Theo c\u00e2u 1, ta \u0111\u00e3 ch\u1ee9ng minh \u0111\u01b0\u1ee3c: $GHIK$ l\u00e0 h\u00ecnh vu\u00f4ng. <br\/> Ta c\u00f3 : $GH=\\dfrac{1}{2}AB=6\\,\\,\\left( cm \\right)$ <br\/> $\\Rightarrow {{S}_{GHIK}}=G{{H}^{2}}=36\\,\\,\\left( c{{m}^{2}} \\right)$ <br\/> Di\u1ec7n t\u00edch ph\u1ea7n h\u00ecnh vu\u00f4ng $ABCD$ n\u1eb1m ngo\u00e0i h\u00ecnh vu\u00f4ng $GHIK$ l\u00e0 : <br\/> $S={{S}_{ABCD}}-{{S}_{GHIK}}$ <br\/> $={{12}^{2}}-36=108\\,\\,\\left( c{{m}^{2}} \\right)$ <br\/> <span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 B. <\/span> <\/span> ","column":3}]}],"id_ques":1640}],"lesson":{"save":0,"level":1}}