Question

2) Tính góc B va góc C của tam giác ABC ,biết :

a, Góc A = 70*

b, Góc B - góc C =10*

c, Góc A = 60* ; góc B = 2 nhân góc C 

Answer 1

a,b:

Tam giác ABC có: \(\widehat{A}+\widehat{B}+\widehat{C}=180^0\)(Định lí tổng 3 góc 1 tam giác)

=> \(70^0+\widehat{B}+\widehat{C}=180^0\)

\(\Rightarrow\widehat{B}+\widehat{C}=110^0\)

MÀ \(\widehat{B}-\widehat{C}=10^0\)

=> \(\widehat{B}=\left(110^0+10^0\right):2=60^0\)

\(\Rightarrow\widehat{C}=60^0-10^0=50^0\)

c, do \(\widehat{A}=60^0\)nên \(\widehat{B}+\widehat{C}=120^0\)

Mặt khác: \(\widehat{B}=2\widehat{C}\)

\(\Rightarrow\widehat{B}+\widehat{C}=2\widehat{C}+\widehat{C}\)

\(\Rightarrow120^0=3\widehat{C}\)

\(\Rightarrow\widehat{C}=40^0\)

\(\Rightarrow\widehat{B}=120^0-40^0=80^0\)