Câu 8. Cho $\triangle$ABC có $\widehat{A}$+$\widehat{B}$=3$\widehat{C}$. Khi đó $\widehat{A}$+$\widehat{B}$- $\widehat{C}$bằng A. $45°$. B. $60^0$. C. $135°$. D. $90°$.

Câu `8:`

Cho `triangle ABC` có `hatA+hatB=3hatC`

Mà `hatA+hatB+hatC=180^@` (tổng `3` góc trong tam giác)

`=>` `3hatC+hatC=180^@`

`=>` `4hatC=180^@`

`=>` `hatC=180^@ : 4`

`=>` `hatC=45^@`

Ta có: `hatA+hatB=3hatC`

`=>` `hatA+hatB=3.45^@`

`=>` `hatA+hatB=125^@`

`=>` `hatA+hatB-hatC=125^@-45^@=90^@`

`=>` Chọn `bb D.`