Question

tam giác ABC có góc A = 180°- 3×góc C

â) chứng minh rằng góc B= 2×góc C

Answer 1

Ta có \(\widehat{A}=180^0-3\times\widehat{C}\)

Mà \(\widehat{A}+\widehat{B}+\widehat{C}=180^0\)(Tổng 3 góc trong tam giác ABC là \(180^0\))

Do đó : \(\widehat{A}+\widehat{B}+\widehat{C}\)

=\(180^0-3\times\widehat{C}+\widehat{B}+\widehat{C}=180^0\)

Vì vậy \(\widehat{B}=180^0-180^0+3\times\widehat{C}-\widehat{C}\)

\(=2\times\widehat{C}\)