hinh hoc 9

V

vitconcatinh_foreverloveyou

Cho tam giac ABC co BC=12cm,gocB=60,goc C=40.Tinh duong cao CH , canh AC VA DIEN TICG TAM GIAC abc


[TEX]\Delta BHC , \hat {B}=60^o \rightarrow \hat{C}=30^o[/TEX]

[TEX]\rightarrow BH=\frac{BC}{2} = 6[/TEX]

ap dung dli pytago

[TEX]\rightarrow HC= \sqrt{108}[/TEX]

[TEX]AC = \frac{HC}{cos 10^o} =.....[/TEX] (cai nay ban tu tinh nha)

tu do tinh HA va AB rui suy ra dt tg ABC
 
A

anh_anh_1321

Cho tam giac ABC co BC=12cm,gocB=60,goc C=40.Tinh duong cao CH , canh AC VA DIEN TICG TAM GIAC abc

[TEX]\triangle\ BCH[/TEX] vuông tại H
[TEX]\Rightarrow HC=BC.sin60^o=6\sqrt{3}\[/TEX]
[TEX]AC={\frac{HC}{cos10^o}}={\frac{6\sqrt{3}}{cos10^o}}\approx\ 10,55[/TEX]
[TEX]AB=AH+HB=AC.sin10^o+{\frac{BC}{2}}={\frac{6\sqrt{3}}{cos10^o}}.sin10^o+6\approx\ 7,83[/TEX]
[TEX]S_{\triangle\ ABC}={\frac{AB.HC}{2}}\approx\40,70[/TEX]
 
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