Ta có: AB = AC => ΔABC cân tại A => \(\widehat{B_1}=\widehat{C_1}=\dfrac{180^o-70^o}{2}=55^o\)

AB = AD => ΔABD cân tại A => \(\widehat{B_1}=\widehat{D_1}=\dfrac{180^o-\left(70^o+\alpha\right)}{2}=\dfrac{110^o-\alpha}{2}\)

AC = AD => ΔACD cân tại A => \(\widehat{D}=\widehat{C_2}=\dfrac{180^o-\alpha}{2}\) <=> \(\dfrac{110^o-\alpha}{2}+x=\dfrac{180^o-\alpha}{2}\Leftrightarrow x=\dfrac{180^o-\alpha-\left(110^o-\alpha\right)}{2}\Leftrightarrow x=35^o\)