Đáp án:
Bài 1:
$\widehat{C}=80^o,\widehat{D}=60^o$
Giải thích các bước giải:
Bài 1:
Ta có:
$\widehat{A}+\widehat{B}+\widehat{C}+\widehat{D}=360^o$
$\rightarrow\widehat{C}+\widehat{D}=360^o- \widehat{A}-\widehat{B}$
$\rightarrow\widehat{C}+\widehat{D}=360^o- 120^o-100^o=140^o$
Mà $\widehat{C}-\widehat{D}=20^o$
$\rightarrow \begin{cases}\widehat{C}=\dfrac{140^o+20^o}{2}=80^o\\\widehat{D}=\dfrac{140^o-20^o}{2}=60^o\end{cases}$