Giải Bài tập 11 trang 58 sgk Toán 11 tập 1 Cánh diều

Ta có: $u_{1}=\widehat{A};u_{2}=\widehat{B}=\widehat{A}+d;u_{3}=\widehat{C}=\widehat{A}+2d;u_{4}=\widehat{D}=\widehat{A}+3d$

Mà: $\widehat{C}=5\widehat{A}=\widehat{A}+2d\Rightarrow d=2\widehat{A}$

Vì: $\widehat{A}+\widehat{B}+\widehat{C}+\widehat{D}=360^{\circ}$$\Leftrightarrow 16\widehat{A}=360^{\circ}\Leftrightarrow \widehat{A}=22,5^{\circ}$

$\Rightarrow \widehat{B}=67,5^{\circ};\widehat{C}=112,5^{\circ};\widehat{D}=157,5^{\circ}$