{"segment":[{"time":24,"part":[{"title":"H\u00e3y ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang","title_trans":"","temp":"multiple_choice","correct":[[4]],"list":[{"point":5,"ques":"\u0110\u1ed9 d\u00e0i cung ${{60}^{o}}$ c\u1ee7a \u0111\u01b0\u1eddng tr\u00f2n c\u00f3 b\u00e1n k\u00ednh $2cm$ l\u00e0:","select":["A. $\\dfrac{\\pi }{3}\\,\\left( cm \\right)$ ","B. $\\dfrac{2}{3\\pi }\\,\\left( cm \\right)$ ","C. $\\dfrac{3\\pi }{2}\\,\\left( cm \\right)$ ","D. $\\dfrac{2\\pi }{3}\\,\\left( cm \\right)$ "],"explain":" <span class='basic_left'> \u00c1p d\u1ee5ng c\u00f4ng th\u1ee9c t\u00ednh \u0111\u1ed9 d\u00e0i cung tr\u00f2n $l=\\dfrac{\\pi Rn}{180}$, ta c\u00f3; <br\/> \u0110\u1ed9 d\u00e0i cung ${{60}^{o}}$ c\u1ee7a \u0111\u01b0\u1eddng tr\u00f2n c\u00f3 b\u00e1n k\u00ednh $2cm$ l\u00e0: <br\/> $l=\\dfrac{\\pi .2.60}{180}=\\dfrac{2\\pi }{3}\\,(cm)$ <br\/><span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 D <\/span><\/span>","column":4}]}],"id_ques":1561},{"time":24,"part":[{"title":"H\u00e3y ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang","title_trans":"","temp":"multiple_choice","correct":[[1]],"list":[{"point":5,"ques":"N\u1ebfu chu vi \u0111\u01b0\u1eddng tr\u00f2n t\u0103ng th\u00eam $10cm$ th\u00ec b\u00e1n k\u00ednh \u0111\u01b0\u1eddng tr\u00f2n t\u0103ng th\u00eam:","select":["A. $\\dfrac{5}{\\pi }\\,\\left( cm \\right)$ ","B. $\\dfrac{\\pi }{5}\\,\\left( cm \\right)$ ","C. $5\\pi \\,\\left( cm \\right)$","D. $\\dfrac{1}{5\\pi }\\,\\left( cm \\right)$ "],"explain":" <span class='basic_left'> G\u1ecdi $x$ l\u00e0 \u0111\u1ed9 d\u00e0i b\u00e1n k\u00ednh \u0111\u01b0\u1eddng tr\u00f2n t\u0103ng l\u00ean, $P$ l\u00e0 chu vi \u0111\u01b0\u1eddng tr\u00f2n ban \u0111\u1ea7u, $R$ l\u00e0 b\u00e1n k\u00ednh ban \u0111\u1ea7u c\u1ee7a \u0111\u01b0\u1eddng tr\u00f2n <br\/> Ta c\u00f3: $2\\pi \\left( R+x \\right)=P+10$ <br\/> $\\Leftrightarrow 2\\pi R+2\\pi x=P+10$ <br\/> $\\Leftrightarrow P+2\\pi x=P+10 \\Leftrightarrow 2\\pi x=10 \\Leftrightarrow x=\\dfrac{5}{\\pi }\\,\\left( cm \\right)$ <br\/><span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 A <\/span><\/span>","column":4}]}],"id_ques":1562},{"time":24,"part":[{"title":"H\u00e3y ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang","title_trans":"","temp":"multiple_choice","correct":[[3]],"list":[{"point":5,"ques":"N\u1ebfu b\u00e1n k\u00ednh \u0111\u01b0\u1eddng tr\u00f2n t\u0103ng th\u00eam $\\dfrac{\\sqrt{2}}{2}\\,\\left( m \\right)$ th\u00ec chu vi \u0111\u01b0\u1eddng tr\u00f2n t\u0103ng th\u00eam: ","select":["A. $\\dfrac{1}{\\pi \\sqrt{2}}\\,\\left( m \\right)$ ","B. $\\dfrac{\\sqrt{2}}{2}\\pi \\,\\left( m \\right)$","C. $\\pi \\sqrt{2}\\,\\left( m \\right)$","D. $2\\sqrt{2}\\,\\left( m \\right)$"],"explain":" <span class='basic_left'> G\u1ecdi $P$ l\u00e0 chu vi \u0111\u01b0\u1eddng tr\u00f2n ban \u0111\u1ea7u, $R$ l\u00e0 b\u00e1n k\u00ednh ban \u0111\u1ea7u c\u1ee7a \u0111\u01b0\u1eddng tr\u00f2n <br\/> Chu vi c\u1ee7a \u0111\u01b0\u1eddng tr\u00f2n l\u00fac sau l\u00e0: <br\/> $2\\pi \\left( R+\\dfrac{\\sqrt{2}}{2} \\right)=2\\pi R+2\\pi .\\dfrac{\\sqrt{2}}{2}=P+\\pi \\sqrt{2}\\,(cm)$ <br\/> Suy ra chu vi \u0111\u01b0\u1eddng tr\u00f2n t\u0103ng th\u00eam $\\pi \\sqrt{2}\\,(cm)$ <br\/><span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 C <\/span><\/span>","column":2}]}],"id_ques":1563},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","temp":"fill_the_blank","correct":[[["4"]]],"list":[{"point":5,"width":50,"type_input":"","ques":" B\u00e1n k\u00ednh \u0111\u01b0\u1eddng tr\u00f2n ngo\u1ea1i ti\u1ebfp l\u1ee5c gi\u00e1c \u0111\u1ec1u c\u1ea1nh $4cm$ l\u00e0_input_ $(cm)$","explain":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop9/toan/hinhhoc/bai18/lv1/img\/h936_D4.png' \/><\/center> <br\/> G\u1ecdi $O$ l\u00e0 t\u00e2m \u0111\u01b0\u1eddng tr\u00f2n ngo\u1ea1i ti\u1ebfp l\u1ee5c gi\u00e1c \u0111\u1ec1u $ABCDEF$ <br\/> Ta c\u00f3: $AB=BC=CD=DE=EF=FA$ (t\u00ednh ch\u1ea5t l\u1ee5c gi\u00e1c \u0111\u1ec1u) <br\/> $\\Rightarrow \\overset\\frown{AB}=\\overset\\frown{BC}=\\overset\\frown{CD}=\\overset\\frown{DE}=\\overset\\frown{EF}=\\overset\\frown{FA}$ (\u0111\u1ecbnh l\u00ed li\u00ean h\u1ec7 gi\u1eefa cung v\u00e0 d\u00e2y) <br\/> M\u00e0 $\\text{s\u0111}\\overset\\frown{AB}+\\text{s\u0111}\\overset\\frown{BC}+\\text{s\u0111}\\overset\\frown{CD}+\\text{s\u0111}\\overset\\frown{DE}+\\text{s\u0111}\\overset\\frown{EF}+\\text{s\u0111}\\overset\\frown{FA}={{360}^{o}}$ (t\u1ed5ng s\u1ed1 \u0111o c\u1ea3 \u0111\u01b0\u1eddng tr\u00f2n) <br\/> $\\Rightarrow 6.\\text{s\u0111}\\overset\\frown{AB}={{360}^{o}}\\Rightarrow \\text{s\u0111}\\overset\\frown{AB}={{60}^{o}}$ <br\/> $\\Rightarrow \\widehat{AOB}={{60}^{o}}$ (\u0111\u1ecbnh l\u00ed g\u00f3c \u1edf t\u00e2m) <br\/> X\u00e9t $\\Delta AOB$ c\u00f3: <br\/> $OA=OB$ (c\u00f9ng b\u1eb1ng b\u00e1n k\u00ednh $(O)$) <br\/> $\\widehat{AOB}={{60}^{o}}$ (ch\u1ee9ng minh tr\u00ean) <br\/> $\\Rightarrow \\Delta AOB$ \u0111\u1ec1u (d\u1ea5u hi\u1ec7u nh\u1eadn bi\u1ebft) <br\/> $\\Rightarrow OB=AB=4\\,\\left( cm \\right)$ <br\/> <span class='basic_pink'> V\u1eady s\u1ed1 c\u1ea7n \u0111i\u1ec1n l\u00e0 $4$ <\/span><\/span> "}]}],"id_ques":1564},{"time":24,"part":[{"title":"\u0110i\u1ec1n (<; >; =) th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","temp":"fill_the_blank","correct":[[["="]]],"list":[{"point":5,"width":50,"ques":" Cho h\u00ecnh v\u1ebd: <br\/> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop9/toan/hinhhoc/bai18/lv1/img\/h936_D5.png' \/><\/center> <br\/> So s\u00e1nh \u0111\u1ed9 d\u00e0i n\u1eeda \u0111\u01b0\u1eddng tr\u00f2n l\u1edbn v\u1edbi t\u1ed5ng \u0111\u1ed9 d\u00e0i hai n\u1eeda \u0111\u01b0\u1eddng tr\u00f2n nh\u1ecf <br\/> <b> \u0110\u00e1p s\u1ed1: <\/b> \u0110\u1ed9 d\u00e0i n\u1eeda \u0111\u01b0\u1eddng tr\u00f2n l\u1edbn _input_ T\u1ed5ng \u0111\u1ed9 d\u00e0i hai n\u1eeda \u0111\u01b0\u1eddng tr\u00f2n nh\u1ecf","explain":" <span class='basic_left'> Ta c\u00f3 b\u00e1n k\u00ednh c\u1ee7a \u0111\u01b0\u1eddng tr\u00f2n \u0111\u01b0\u1eddng k\u00ednh $AB$ l\u00e0 $\\dfrac{AB}{2}$ <br\/> B\u00e1n k\u00ednh c\u1ee7a \u0111\u01b0\u1eddng tr\u00f2n \u0111\u01b0\u1eddng k\u00ednh $AD$ l\u00e0 $\\dfrac{3AB}{8}$ <br\/> B\u00e1n k\u00ednh c\u1ee7a \u0111\u01b0\u1eddng tr\u00f2n \u0111\u01b0\u1eddng k\u00ednh $BD$ l\u00e0 $\\dfrac{AB}{8}$ <br\/> \u0110\u1ed9 d\u00e0i c\u1ee7a n\u1eeda \u0111\u01b0\u1eddng tr\u00f2n \u0111\u01b0\u1eddng k\u00ednh $AB$ l\u00e0 $C=\\pi .\\dfrac{AB}{2}$ (\u0111v\u0111d) <br\/> \u0110\u1ed9 d\u00e0i c\u1ee7a n\u1eeda \u0111\u01b0\u1eddng tr\u00f2n \u0111\u01b0\u1eddng k\u00ednh $AD$ l\u00e0 ${{C}_{1}}=\\pi .\\dfrac{3AB}{8}$ (\u0111v\u0111d) <br\/> \u0110\u1ed9 d\u00e0i c\u1ee7a n\u1eeda \u0111\u01b0\u1eddng tr\u00f2n \u0111\u01b0\u1eddng k\u00ednh $BD$ l\u00e0 ${{C}_{2}}=\\pi .\\dfrac{AB}{8}$ (\u0111vdt) <br\/> Ta c\u00f3: $\\dfrac{3\\pi .AB}{8}+\\dfrac{\\pi .AB}{8}=\\dfrac{\\pi .AB}{2}$ <br\/> $\\Rightarrow C={{C}_{1}}+{{C}_{2}}$ <br\/> Suy ra \u0111\u1ed9 d\u00e0i n\u1eeda \u0111\u01b0\u1eddng tr\u00f2n l\u1edbn b\u1eb1ng t\u1ed5ng \u0111\u1ed9 d\u00e0i hai n\u1eeda \u0111\u01b0\u1eddng tr\u00f2n nh\u1ecf <br\/> <span class='basic_pink'> V\u1eady d\u1ea5u c\u1ea7n \u0111i\u1ec1n l\u00e0 $=$ <\/span><\/span> "}]}],"id_ques":1565},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","temp":"fill_the_blank","correct":[[["4"]]],"list":[{"point":5,"width":50,"type_input":"","ques":" Cho h\u00ecnh v\u1ebd:<br\/> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop9/toan/hinhhoc/bai18/lv1/img\/h936_D6.png' \/><\/center> <br\/> Trong \u0111\u00f3 $ABCD$ l\u00e0 h\u00ecnh vu\u00f4ng c\u1ea1nh $4cm$. Khi \u0111\u00f3, t\u1ed5ng \u0111\u1ed9 d\u00e0i c\u00e1c \u0111\u01b0\u1eddng cong l\u00e0 _input_ $\\pi \\,(cm)$","explain":" <span class='basic_left'> Nh\u1eadn th\u1ea5y b\u1ed1n h\u00ecnh qu\u1ea1t t\u1ea1o th\u00e0nh m\u1ed9t \u0111\u01b0\u1eddng tr\u00f2n b\u00e1n k\u00ednh $2cm$ <br\/> \u0110\u1ed9 d\u00e0i \u0111\u01b0\u1eddng tr\u00f2n b\u00e1n k\u00ednh $2cm$ l\u00e0: <br\/> $C=2\\pi R=2\\pi .2=4\\pi \\,\\left( cm \\right)$ <br\/> <span class='basic_pink'> V\u1eady s\u1ed1 c\u1ea7n \u0111i\u1ec1n l\u00e0 $4$ <\/span><\/span> "}]}],"id_ques":1566},{"time":24,"part":[{"title":"H\u00e3y ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang","title_trans":"","temp":"multiple_choice","correct":[[3]],"list":[{"point":5,"ques":"<span class='basic_left'> H\u00ecnh n\u00e0o trong c\u00e1c h\u00ecnh sau kh\u00f4ng th\u1ecfa m\u00e3n: Lu\u00f4n c\u00f3 m\u1ed9t v\u00e0 ch\u1ec9 m\u1ed9t \u0111\u01b0\u1eddng tr\u00f2n ngo\u1ea1i ti\u1ebfp v\u00e0 c\u00f3 m\u1ed9t v\u00e0 ch\u1ec9 m\u1ed9t \u0111\u01b0\u1eddng tr\u00f2n n\u1ed9i ti\u1ebfp?","select":["A. Tam gi\u00e1c \u0111\u1ec1u ","B. H\u00ecnh vu\u00f4ng ","C. Ng\u0169 gi\u00e1c","D. L\u1ee5c gi\u00e1c \u0111\u1ec1u"],"explain":" <span class='basic_left'> Ta c\u00f3: B\u1ea5t k\u00ec \u0111a gi\u00e1c \u0111\u1ec1u n\u00e0o c\u0169ng c\u00f3 m\u1ed9t v\u00e0 ch\u1ec9 m\u1ed9t \u0111\u01b0\u1eddng tr\u00f2n ngo\u1ea1i ti\u1ebfp v\u00e0 c\u00f3 m\u1ed9t v\u00e0 ch\u1ec9 m\u1ed9t \u0111\u01b0\u1eddng tr\u00f2n n\u1ed9i ti\u1ebfp <br\/> H\u00ecnh vu\u00f4ng l\u00e0 t\u1ee9 gi\u00e1c \u0111\u1ec1u n\u00ean tam gi\u00e1c \u0111\u1ec1u, h\u00ecnh vu\u00f4ng v\u00e0 l\u1ee5c gi\u00e1c \u0111\u1ec1u l\u00e0 \u0111\u00e1p \u00e1n \u0111\u00fang <br\/> Suy ra \u0111\u00e1p \u00e1n C kh\u00f4ng \u0111\u00fang. <br\/><span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 C <\/span><\/span>","column":2}]}],"id_ques":1567},{"time":24,"part":[{"title":"H\u00e3y ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang","title_trans":"","temp":"multiple_choice","correct":[[2]],"list":[{"point":5,"ques":"Cho m\u1ed9t tam gi\u00e1c \u0111\u1ec1u. T\u1ec9 s\u1ed1 gi\u1eefa b\u00e1n k\u00ednh c\u1ee7a \u0111\u01b0\u1eddng tr\u00f2n n\u1ed9i ti\u1ebfp v\u00e0 \u0111\u01b0\u1eddng tr\u00f2n ngo\u1ea1i ti\u1ebfp tam gi\u00e1c \u0111\u00f3 b\u1eb1ng: ","select":["A. $\\dfrac{1}{4}$ ","B. $\\dfrac{1}{2}$ ","C. $\\dfrac{1}{3}$","D. $\\dfrac{2}{3}$"],"explain":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop9/toan/hinhhoc/bai18/lv1/img\/h936_D8.png' \/><\/center> <br\/> Ta c\u00f3: T\u00e2m c\u1ee7a \u0111\u01b0\u1eddng tr\u00f2n n\u1ed9i ti\u1ebfp tam gi\u00e1c \u0111\u1ec1u tr\u00f9ng v\u1edbi t\u00e2m c\u1ee7a \u0111\u01b0\u1eddng tr\u00f2n ngo\u1ea1i ti\u1ebfp tr\u00f9ng v\u1edbi tr\u1ecdng t\u00e2m tam gi\u00e1c <br\/> G\u1ecdi tam gi\u00e1c \u0111\u1ec1u l\u00e0 $ABC$, c\u00f3 tr\u1ecdng t\u00e2m $G$, trung tuy\u1ebfn $AH$ <br\/> Gi\u1ea3 s\u1eed $R$ l\u00e0 b\u00e1n k\u00ednh \u0111\u01b0\u1eddng tr\u00f2n ngo\u1ea1i ti\u1ebfp tam gi\u00e1c, $r$ l\u00e0 b\u00e1n k\u00ednh \u0111\u01b0\u1eddng tr\u00f2n n\u1ed9i ti\u1ebfp tam gi\u00e1c th\u00ec: <br\/> $AG=R=\\dfrac{2}{3}AH$; $HG=r=\\dfrac{1}{3}AH$ (t\u00ednh ch\u1ea5t tr\u1ecdng t\u00e2m tam gi\u00e1c) <br\/> $\\Rightarrow \\dfrac{r}{R}=\\dfrac{1}{3}AH:\\left( \\dfrac{2}{3}AH \\right)=\\dfrac{1}{2}$ <br\/><span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 B <\/span><\/span>","column":4}]}],"id_ques":1568},{"time":24,"part":[{"title":"H\u00e3y ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang","title_trans":"","temp":"multiple_choice","correct":[[2]],"list":[{"point":5,"ques":"M\u1ed9t tam gi\u00e1c \u0111\u1ec1u c\u00f3 c\u1ea1nh b\u1eb1ng $2cm$. \u0110\u1ed9 d\u00e0i \u0111\u01b0\u1eddng tr\u00f2n n\u1ed9i ti\u1ebfp tam gi\u00e1c \u0111\u00f3 b\u1eb1ng: ","select":["A. $\\pi \\,\\left( cm \\right)$","B. $\\dfrac{2\\pi }{\\sqrt{3}}\\,\\left( cm \\right)$ ","C. $\\dfrac{2\\pi }{3}\\,\\left( cm \\right)$","D. $\\dfrac{\\pi }{\\sqrt{3}}\\,\\left( cm \\right)$"],"explain":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop9/toan/hinhhoc/bai18/lv1/img\/h936_D9.png' \/><\/center> <br\/> G\u1ecdi $ABC$ l\u00e0 tam gi\u00e1c \u0111\u1ec1u c\u1ea1nh $2cm$, $H$ l\u00e0 trung \u0111i\u1ec3m c\u1ee7a $BC$ <br\/>$\\Rightarrow AH$ l\u00e0 tia ph\u00e2n gi\u00e1c c\u1ee7a g\u00f3c $\\widehat{BAC}$ <br\/> $\\Rightarrow \\widehat{BAH}=\\dfrac{1}{2}\\widehat{BAC}={{30}^{o}},\\widehat{AHB}={{90}^{o}}$ <br\/> X\u00e9t $\\Delta AHB$ vu\u00f4ng t\u1ea1i $H$ c\u00f3: <br\/> $\\Rightarrow AH=AB.cos\\widehat{AHB}=2.\\cos {{30}^{o}}=\\sqrt{3}\\,\\left( cm \\right)$ <br\/> B\u00e1n k\u00ednh \u0111\u01b0\u1eddng tr\u00f2n n\u1ed9i ti\u1ebfp tam gi\u00e1c l\u00e0: <br\/> $r=\\dfrac{AH}{3}=\\dfrac{\\sqrt{3}}{3}=\\dfrac{1}{\\sqrt{3}}\\,\\left( cm \\right)$ <br\/> \u0110\u1ed9 d\u00e0i \u0111\u01b0\u1eddng tr\u00f2n n\u1ed9i ti\u1ebfp tam gi\u00e1c l\u00e0: <br\/> $C=2\\pi .r=\\dfrac{2\\pi }{\\sqrt{3}}\\,\\left( cm \\right)$ <br\/><span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 B <\/span><\/span>","column":4}]}],"id_ques":1569},{"time":24,"part":[{"title":"H\u00e3y ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang","title_trans":"","temp":"multiple_choice","correct":[[1]],"list":[{"point":5,"ques":"Cung $AB$ c\u1ee7a m\u1ed9t \u0111\u01b0\u1eddng tr\u00f2n b\u00e1n k\u00ednh $R$ c\u00f3 \u0111\u1ed9 d\u00e0i b\u1eb1ng $\\dfrac{\\pi R}{6}.$ S\u1ed1 \u0111o cung $AB$ b\u1eb1ng: ","select":["A. ${{30}^{o}}$","B. ${{45}^{o}}$ ","C. ${{60}^{o}}$","D. ${{90}^{o}}$"],"explain":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop9/toan/hinhhoc/bai18/lv1/img\/h936_D10.png' \/><\/center> <br\/> Ta c\u00f3: \u0110\u1ed9 d\u00e0i cung tr\u00f2n ${{n}^{o}}$ c\u1ee7a \u0111\u01b0\u1eddng tr\u00f2n b\u00e1n k\u00ednh $R$ l\u00e0: $l=2\\pi R.\\dfrac{n}{360}$ <br\/> $ \\Leftrightarrow n=\\dfrac{360.l}{2\\pi R}=\\dfrac{360.\\dfrac{\\pi R}{6}}{2\\pi R}={{30}^{o}}$ <br\/><span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 A <\/span><\/span>","column":4}]}],"id_ques":1570},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","temp":"fill_the_blank","correct":[[["60"]]],"list":[{"point":5,"width":50,"type_input":"","ques":"<span class='basic_left'> M\u1ed9t \u0111\u01b0\u1eddng tr\u00f2n t\u00e2m $O$ c\u00f3 chu vi l\u00e0 $36\\pi$, cung $AB$ tr\u00ean \u0111\u01b0\u1eddng tr\u00f2n \u0111\u00f3 c\u00f3 \u0111\u1ed9 d\u00e0i $6\\pi$. T\u00ednh g\u00f3c $AOB$. <br\/> <b> \u0110\u00e1p s\u1ed1: <\/b> $\\widehat{AOB}=$ _input_ $^o$","explain":" <span class='basic_left'><center><img src='https://www.luyenthi123.com/file/luyenthi123/lop9/toan/hinhhoc/bai18/lv1/img\/h936_D10.png' \/><\/center> <br\/> S\u1ed1 \u0111o cung $AB$ l\u00e0: <br\/> $n=\\dfrac{180.l}{\\pi R}=\\dfrac{360.l}{2\\pi R}=\\dfrac{360.6\\pi }{36\\pi }=60$ <br\/> Do \u0111\u00f3 $\\widehat{AOB}=\\text{s\u0111}\\overset\\frown{AB}={{60}^{o}}$ <br\/> <span class='basic_pink'> V\u1eady s\u1ed1 c\u1ea7n \u0111i\u1ec1n l\u00e0 $60$ <\/span><\/span> "}]}],"id_ques":1571},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","temp":"fill_the_blank","correct":[[["6369,4"]]],"list":[{"point":5,"width":50,"type_input":"","ques":"X\u00edch \u0110\u1ea1o l\u00e0 m\u1ed9t \u0111\u01b0\u1eddng tr\u00f2n l\u1edbn c\u1ee7a Tr\u00e1i \u0110\u1ea5t c\u00f3 \u0111\u1ed9 d\u00e0i kho\u1ea3ng $40000km$. B\u00e1n k\u00ednh c\u1ee7a Tr\u00e1i \u0110\u1ea5t l\u00e0 (l\u1ea5y gi\u00e1 tr\u1ecb g\u1ea7n \u0111\u00fang c\u1ee7a $\\pi$ l\u00e0 $3,14$ v\u00e0 l\u00e0m tr\u00f2n \u0111\u1ebfn ch\u1eef s\u1ed1 th\u1eadp ph\u00e2n th\u1ee9 nh\u1ea5t) <br\/> <b> \u0110\u00e1p s\u1ed1: <\/b> B\u00e1n k\u00ednh c\u1ee7a Tr\u00e1i \u0110\u1ea5t l\u00e0: _input_ $(km)$","explain":" <span class='basic_left'>\u0110\u1ed9 d\u00e0i c\u1ee7a X\u00edch \u0110\u1ea1o l\u00e0 chu vi c\u1ee7a \u0111\u01b0\u1eddng tr\u00f2n l\u1edbn c\u1ee7a Tr\u00e1i \u0110\u1ea5t <br\/> G\u1ecdi $R$ l\u00e0 b\u00e1n k\u00ednh Tr\u00e1i \u0110\u1ea5t, ta c\u00f3: <br\/> $C=2\\pi R\\Leftrightarrow 40000=2\\pi R \\\\ \\Leftrightarrow R=\\dfrac{40000}{2\\pi }\\approx \\dfrac{40000}{2.3,14}=6369,4\\,\\left( km \\right)$ <br\/> <span class='basic_pink'> V\u1eady s\u1ed1 c\u1ea7n \u0111i\u1ec1n l\u00e0 $6369,4$ <\/span><\/span> "}]}],"id_ques":1572},{"time":24,"part":[{"title":"\u0110i\u1ec1n d\u1ea5u (>; <; =) th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","temp":"fill_the_blank","correct":[[["="]]],"list":[{"point":5,"width":50,"type_input":"","ques":"<span class='basic_left'> Cho h\u00ecnh v\u1ebd, <br\/> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop9/toan/hinhhoc/bai18/lv1/img\/h936_D11.png' \/><\/center> <br\/> G\u1ecdi $C$ l\u00e0 t\u1ed5ng \u0111\u1ed9 d\u00e0i ba n\u1eeda \u0111\u01b0\u1eddng tr\u00f2n tr\u00ean h\u00ecnh 1 v\u00e0 $C\u2019$ l\u00e0 t\u1ed5ng \u0111\u1ed9 d\u00e0i n\u0103m n\u1eeda \u0111\u01b0\u1eddng tr\u00f2n tr\u00ean h\u00ecnh 2. H\u00e3y so s\u00e1nh $C$ v\u00e0 $C\u2019$ bi\u1ebft $AD = EK$. <br\/> <b> \u0110\u00e1p s\u1ed1 <\/b> $C$ _input_ $C\u2019$ ","explain":" <span class='basic_left'> Ta c\u00f3: <br\/> $\\begin{align} C&=\\dfrac{AB.\\pi }{2}+\\dfrac{BC.\\pi }{2}+\\dfrac{CD.\\pi }{2}\\\\&=\\dfrac{\\left( AB+BC+CD \\right).\\pi }{2}\\\\ &=\\dfrac{AD.\\pi }{2} \\end{align}$ <br\/> $\\begin{align} C'&=\\dfrac{EF.\\pi }{2}+\\dfrac{FG.\\pi }{2}+\\dfrac{GH.\\pi }{2}+\\dfrac{HI.\\pi }{2}+\\dfrac{IK.\\pi }{2}\\\\&=\\dfrac{\\left( EF+FG+GH+HI+IK \\right).\\pi }{2}\\\\&=\\dfrac{EK.\\pi }{2} \\end{align}$ <br\/> M\u00e0 $AD=EK\\Rightarrow C=C'$ <br\/> <span class='basic_pink'> V\u1eady d\u1ea5u c\u1ea7n \u0111i\u1ec1n l\u00e0 $=$ <\/span><\/span> "}]}],"id_ques":1573},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","temp":"fill_the_blank","correct":[[["133"]]],"list":[{"point":5,"width":50,"type_input":"","ques":"<span class='basic_left'> B\u00e1nh xe c\u1ee7a m\u1ed9t r\u00f2ng r\u1ecdc c\u00f3 chu vi $540mm$. D\u00e2y cua-roa bao b\u00e1nh xe theo cung $AB$ c\u00f3 \u0111\u1ed9 d\u00e0i $200mm$. T\u00ednh g\u00f3c $AOB$ (l\u00e0m tr\u00f2n \u0111\u1ebfn \u0111\u01a1n v\u1ecb \u0111\u1ed9) <br\/> <b> \u0110\u00e1p s\u1ed1: <\/b> $\\widehat{AOB} = $ _input_ $^o$","explain":" <span class='basic_left'> <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop9/toan/hinhhoc/bai18/lv1/img\/h936_D14.png' \/><\/center> \u00c1p d\u1ee5ng c\u00f4ng th\u1ee9c $l=\\dfrac{\\pi Rn}{180}$ <br\/> $\\Rightarrow n=\\dfrac{180.l}{\\pi R}=\\dfrac{360.l}{2\\pi R}=\\dfrac{360.200}{540}\\approx 133$ <br\/> $\\Rightarrow \\widehat{AOB}=\\text{s\u0111}\\overset\\frown{AB}={{133}^{o}}$ <br\/> <span class='basic_pink'> V\u1eady s\u1ed1 c\u1ea7n \u0111i\u1ec1n l\u00e0 $133$ <\/span><\/span> "}]}],"id_ques":1574},{"time":9,"part":[{"title":"L\u1ef1a ch\u1ecdn \u0111\u00fang hay sai","title_trans":"L\u1ef1a ch\u1ecdn \u0111\u00fang hay sai","temp":"true_false","correct":[["t","f","f","t"]],"list":[{"point":10,"col_name":["","\u0110\u00fang","Sai"],"arr_ques":["\u0110a gi\u00e1c \u0111\u1ec1u th\u00ec n\u1ed9i ti\u1ebfp \u0111\u01b0\u1ee3c m\u1ed9t \u0111\u01b0\u1eddng tr\u00f2n ","\u0110a gi\u00e1c n\u1ed9i ti\u1ebfp \u0111\u01b0\u1ee3c m\u1ed9t \u0111\u01b0\u1eddng tr\u00f2n l\u00e0 \u0111a gi\u00e1c \u0111\u1ec1u","\u0110a gi\u00e1c ngo\u1ea1i ti\u1ebfp \u0111\u01b0\u1ee3c m\u1ed9t \u0111\u01b0\u1eddng tr\u00f2n l\u00e0 m\u1ed9t \u0111a gi\u00e1c \u0111\u1ec1u","\u0110a gi\u00e1c \u0111\u1ec1u th\u00ec ngo\u1ea1i ti\u1ebfp \u0111\u01b0\u1ee3c m\u1ed9t \u0111\u01b0\u1eddng tr\u00f2n"],"explain":["\u0110\u00fang, b\u1ea5t k\u00ec \u0111a gi\u00e1c \u0111\u1ec1u n\u00e0o c\u0169ng c\u00f3 m\u1ed9t v\u00e0 ch\u1ec9 m\u1ed9t \u0111\u01b0\u1eddng tr\u00f2n ngo\u1ea1i ti\u1ebfp v\u00e0 c\u00f3 m\u1ed9t v\u00e0 ch\u1ec9 m\u1ed9t \u0111\u01b0\u1eddng tr\u00f2n n\u1ed9i ti\u1ebfp (\u0111\u1ecbnh l\u00ed)","Sai, v\u00ed d\u1ee5 tam gi\u00e1c nh\u1ecdn, t\u1ee9 gi\u00e1c \u2026 v\u1eabn c\u00f3 th\u1ec3 n\u1ed9i ti\u1ebfp \u0111\u01b0\u1ee3c trong m\u1ed9t \u0111\u01b0\u1eddng tr\u00f2n","Sai, v\u00ed d\u1ee5 minh h\u1ecda <center><img src='https://www.luyenthi123.com/file/luyenthi123/lop9/toan/hinhhoc/bai18/lv1/img\/h936_D15.png' \/><\/center>","\u0110\u00fang, b\u1ea5t k\u00ec \u0111a gi\u00e1c \u0111\u1ec1u n\u00e0o c\u0169ng c\u00f3 m\u1ed9t v\u00e0 ch\u1ec9 m\u1ed9t \u0111\u01b0\u1eddng tr\u00f2n ngo\u1ea1i ti\u1ebfp v\u00e0 c\u00f3 m\u1ed9t v\u00e0 ch\u1ec9 m\u1ed9t \u0111\u01b0\u1eddng tr\u00f2n n\u1ed9i ti\u1ebfp (\u0111\u1ecbnh l\u00ed)"]}]}],"id_ques":1575},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","temp":"fill_the_blank","correct":[[["680"]]],"list":[{"point":5,"width":50,"type_input":"","ques":"T\u00ednh chu vi c\u1ee7a m\u1ed9t v\u00e0nh xe \u0111\u1ea1p c\u00f3 \u0111\u01b0\u1eddng k\u00ednh $680mm$. (l\u00e0m tr\u00f2n \u0111\u1ebfn h\u00e0ng \u0111\u01a1n v\u1ecb) <br\/> <b> \u0110\u00e1p s\u1ed1: <\/b> Chu vi c\u1ee7a v\u00e0nh xe l\u00e0 _input_ $\\pi\\,(mm)$","explain":" Chu vi v\u00e0nh xe \u0111\u1ea1p c\u00f3 \u0111\u01b0\u1eddng k\u00ednh $680mm$ l\u00e0: <br\/> $C=\\pi d=680.\\pi\\,\\left( mm \\right)$ <br\/> <span class='basic_pink'> V\u1eady s\u1ed1 c\u1ea7n \u0111i\u1ec1n l\u00e0 $680$ <\/span><\/span> "}]}],"id_ques":1576},{"time":24,"part":[{"title":"H\u00e3y ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang","title_trans":"","temp":"multiple_choice","correct":[[2]],"list":[{"point":5,"ques":"C\u1ea1nh b\u00ean c\u1ee7a m\u1ed9t tam gi\u00e1c c\u00e2n b\u1eb1ng $8dm$, g\u00f3c \u1edf \u0111\u1ec9nh c\u1ee7a tam gi\u00e1c b\u1eb1ng $120^o$. T\u00ednh \u0111\u1ed9 d\u00e0i \u0111\u01b0\u1eddng tr\u00f2n ngo\u1ea1i ti\u1ebfp tam gi\u00e1c \u0111\u00f3. ","select":["A. $8\\pi \\,\\left( dm \\right)$","B. $16\\pi \\,\\left( dm \\right)$ ","C. $32\\pi \\,\\left( dm \\right)$","D. $64\\pi \\,\\left( dm \\right)$"],"explain":" <span class='basic_left'> <span class='basic_left'><span class='basic_green'>H\u01b0\u1edbng d\u1eabn:<\/span><br\/>Ch\u1ee9ng minh tam gi\u00e1c $AOB$ \u0111\u1ec3 t\u00ecm b\u00e1n k\u00ednh c\u1ee7a \u0111\u01b0\u1eddng tr\u00f2n ngo\u1ea1i ti\u1ebfp r\u1ed3i \u00e1p d\u1ee5ng c\u00f4ng th\u1ee9c \u0111\u1ed9 d\u00e0i \u0111\u01b0\u1eddng tr\u00f2n gi\u1ea3i b\u00e0i to\u00e1n <\/span> <br\/><center><img src='https://www.luyenthi123.com/file/luyenthi123/lop9/toan/hinhhoc/bai18/lv1/img\/h936_D17.png' \/><\/center> <br\/> <span class='basic_green'>B\u00e0i gi\u1ea3i:<\/span><br\/> Gi\u1ea3 s\u1eed tam gi\u00e1c $ABC$ c\u00e2n t\u1ea1i $A$ c\u00f3: <br\/> $\\widehat{A}={{120}^{o}},AB=AC=8dm$ <br\/> $\\Rightarrow \\widehat{ABC}=\\widehat{ACB}={{30}^{o}}$ <br\/> G\u1ecdi $O$ l\u00e0 t\u00e2m \u0111\u01b0\u1eddng tr\u00f2n ngo\u1ea1i ti\u1ebfp tam gi\u00e1c $ABC$ ta c\u00f3: <br\/> $\\widehat{AOB}=2\\widehat{ACB}={{2.30}^{o}}={{60}^{o}}$ <br\/> $\\Rightarrow \\Delta AOB$ \u0111\u1ec1u <br\/> $\\Rightarrow OA=AB=8\\,\\left( dm \\right)$ <br\/> $\\Rightarrow C=2\\pi R=2\\pi .8=16\\pi \\,\\left( dm \\right)$ <br\/><span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 B <\/span><\/span>","column":4}]}],"id_ques":1577},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","temp":"fill_the_blank","correct":[[["9"],["4"],["10"],["8"],["31,4"],["56,52"]]],"list":[{"point":5,"width":50,"type_input":"","ques":"L\u1ea5y gi\u00e1 tr\u1ecb g\u1ea7n \u0111\u00fang c\u1ee7a $\\pi$ l\u00e0 $3,14$, h\u00e3y \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng trong b\u1ea3ng sau: <br\/> <table><tr><td>B\u00e1n k\u00ednh \u0111\u01b0\u1eddng tr\u00f2n<\/td><td>$5 cm$<\/td><td>_input_$cm$<\/td><td>_input_$cm$<\/td><\/tr><tr><td>\u0110\u01b0\u1eddng k\u00ednh \u0111\u01b0\u1eddng tr\u00f2n<\/td><td>_input_$cm$<\/td><td>$18cm$<\/td><td>_input_$cm$<\/td><\/tr><tr><td>\u0110\u1ed9 d\u00e0i \u0111\u01b0\u1eddng tr\u00f2n<\/td><td>_input_$cm$<\/td><td>_input_$cm$<\/td><td>$25,12 cm$<\/td><\/tr><\/table>","explain":" <span class='basic_left'> Ta c\u00f3: $r=5cm\\Rightarrow d=2.5=10cm;\\,C=10.3,14=31,4\\,\\left( cm \\right)$ <br\/> $d=18cm\\Rightarrow r=18:2=9\\,\\left( cm \\right);\\,C=18.3,14=56,52\\,\\left( cm \\right)$ <br\/> $C=25,12\\,\\left( cm \\right)\\Rightarrow d=25,12:3,14=8\\,\\left( cm \\right)\\Rightarrow r=8:2=4\\,\\left( cm \\right)$ <br\/> Ta c\u00f3 b\u1ea3ng k\u1ebft qu\u1ea3 sau: <br\/> <table><tr><td>B\u00e1n k\u00ednh \u0111\u01b0\u1eddng tr\u00f2n<\/td><td>$5 cm$<\/td><td>$9 cm$<\/td><td>$4 cm$<\/td><\/tr><tr><td>\u0110\u01b0\u1eddng k\u00ednh \u0111\u01b0\u1eddng tr\u00f2n<\/td><td>$ 10 cm$<\/td><td>$18cm$<\/td><td>$8 cm$<\/td><\/tr><tr><td>\u0110\u1ed9 d\u00e0i \u0111\u01b0\u1eddng tr\u00f2n<\/td><td>$31,4 cm$<\/td><td>$56, 52 cm$<\/td><td>$25,12 cm$<\/td><\/tr><\/table><br\/> <span class='basic_pink'> V\u1eady c\u00e1c k\u1ebft qu\u1ea3 c\u1ea7n \u0111i\u1ec1n theo th\u1ee9 t\u1ef1 t\u1eeb tr\u00e1i sang ph\u1ea3i t\u1eeb tr\u00ean xu\u1ed1ng d\u01b0\u1edbi l\u00e0 $9;4;10;8;31,4;56,52$ <\/span><\/span> "}]}],"id_ques":1578},{"time":24,"part":[{"title":"\u0110i\u1ec1n s\u1ed1 th\u00edch h\u1ee3p v\u00e0o ch\u1ed7 tr\u1ed1ng","temp":"fill_the_blank","correct":[[["40,8"],["21,1"],["57"],["15,7"]]],"list":[{"point":5,"width":50,"type_input":"","ques":" L\u1ea5y gi\u00e1 tr\u1ecb g\u1ea7n \u0111\u00fang c\u1ee7a $pi$ l\u00e0 $3,14$, h\u00e3y \u0111i\u1ec1n v\u00e0o \u00f4 tr\u1ed1ng trong b\u1ea3ng sau (l\u00e0m tr\u00f2n \u0111\u1ebfn s\u1ed1 th\u1eadp th\u1ee9 nh\u1ea5t v\u00e0 l\u00e0m tr\u00f2n \u0111\u1ebfn \u0111\u1ed9)<br\/> <table><tr><td>B\u00e1n k\u00ednh \u0111\u01b0\u1eddng tr\u00f2n<\/td><td>$10cm$<\/td><td>_input_$cm$<\/td><td>$21cm$<\/td><td>_input_$cm$<\/td><\/tr><tr><td>S\u1ed1 \u0111o c\u1ee7a cung tr\u00f2n $n^o$<\/td><td>$90^o$<\/td><td>$50^o$<\/td><td>_input_$^o$<\/td><td>$25^o$<\/td><\/tr><tr><td>\u0110\u1ed9 d\u00e0i cung tr\u00f2n $l$<\/td><td>_input_$cm$<\/td><td>$35,6 cm$<\/td><td>$20,8cm$<\/td><td>$9, 2cm$<\/td><\/tr><\/table>","explain":" <span class='basic_left'>Ta c\u00f3: $l=\\dfrac{\\pi Rn}{180}=\\dfrac{3,14.10.90}{180}=15,7\\,\\left( cm \\right)$ <br\/> $R=\\dfrac{180.l}{\\pi n}=\\dfrac{180.35,6}{3,14.50}=40,8\\,\\left( cm \\right)$ <br\/> $n=\\dfrac{180.l}{\\pi R}=\\dfrac{180.20,8}{3,14.21}={{57}^{o}}$ <br\/> $R=\\dfrac{180.l}{\\pi n}=\\dfrac{180.9,2}{3,14.25}=21,1\\,\\left( cm \\right)$ <br\/> Ta c\u00f3 b\u1ea3ng k\u1ebft qu\u1ea3 sau <br\/> <table><tr><td>B\u00e1n k\u00ednh \u0111\u01b0\u1eddng tr\u00f2n<\/td><td>$10cm$<\/td><td>$40,8 cm$<\/td><td>$21cm$<\/td><td>$21,1 cm$<\/td><\/tr><tr><td>S\u1ed1 \u0111o c\u1ee7a cung tr\u00f2n $n^o$<\/td><td>$90^o$<\/td><td>$50^o$<\/td><td>$57^o$<\/td><td>$25^o$<\/td><\/tr><tr><td>\u0110\u1ed9 d\u00e0i cung tr\u00f2n $l$<\/td><td>$15,7cm$<\/td><td>$35,6 cm$<\/td><td>$20,8cm$<\/td><td>$9, 2cm$<\/td><\/tr><\/table> <br\/> <span class='basic_pink'> V\u1eady c\u00e1c k\u1ebft qu\u1ea3 c\u1ea7n \u0111i\u1ec1n theo th\u1ee9 t\u1ef1 t\u1eeb tr\u00e1i sang ph\u1ea3i t\u1eeb tr\u00ean xu\u1ed1ng d\u01b0\u1edbi l\u00e0 $40,8; 21,1; 57; 15,7$ <\/span><\/span> "}]}],"id_ques":1579},{"time":24,"part":[{"title":"H\u00e3y ch\u1ecdn \u0111\u00e1p \u00e1n \u0111\u00fang","title_trans":"","temp":"multiple_choice","correct":[[2]],"list":[{"point":5,"ques":"Cho \u0111\u01b0\u1eddng tr\u00f2n $(O; 2,5cm)$ \u0111\u01b0\u1eddng k\u00ednh $AB$, $C$ l\u00e0 m\u1ed9t \u0111i\u1ec3m tr\u00ean \u0111\u01b0\u1eddng tr\u00f2n sao cho g\u00f3c $BOC = 60^o$. \u0110\u1ed9 d\u00e0i cung $AC$ l\u00e0: ","select":["A. $\\dfrac{3\\pi }{5}\\,\\left( cm \\right)$","B. $\\dfrac{5\\pi }{3}(cm)$ ","C. $\\dfrac{5\\sqrt{3}}{2}cm$","D. $\\dfrac{\\sqrt{3}}{3}\\,\\left( cm \\right)$"],"explain":" <span class='basic_left'><center><img src='https://www.luyenthi123.com/file/luyenthi123/lop9/toan/hinhhoc/bai18/lv1/img\/h936_D20.png' \/><\/center> <br\/> Ta c\u00f3 $\\widehat{AOC}={{180}^{o}}-\\widehat{BOC}={{180}^{o}}-{{60}^{o}}={{120}^{o}}$ <br\/> $l=\\dfrac{\\pi Rn}{180}=\\dfrac{\\pi .2,5.120}{180}=\\dfrac{5\\pi }{3}\\,\\left( cm \\right)$ <br\/><span class='basic_pink'> V\u1eady \u0111\u00e1p \u00e1n l\u00e0 B <\/span><\/span>","column":4}]}],"id_ques":1580}],"lesson":{"save":0,"level":1}}