Đáp án:
a)
Ta có:
$\widehat{ACB}=\widehat{CAD}+\widehat{CDA}=2\widehat{CDA}$
$\widehat{ABC}=2\widehat{ACB}=2.2\widehat{CDA}=4\widehat{CDA}$
$\widehat{BAx}=\widehat{ACB}+\widehat{ABC}=2\widehat{CDA}+4\widehat{CDA}=6\widehat{CDA}$
b)
Xét $\triangle ABC$ có
$\widehat{A}+\hat{B}+\hat{C}=180^0$
$\Rightarrow \widehat{A}+2\hat{C}+\hat{C}=180^0$
$\Rightarrow \widehat{A}+3\hat{C}=180^0$
$\hat{C}=\dfrac{180^0-\hat{A}}{3}=50^0$
$\widehat{CAD}=\dfrac{1}{2}\hat{C}=25^0$
