a) Vì \(\Delta ABC\) cân tại \(A\left(gt\right)\)
=> \(\widehat{ABC}=\widehat{ACB}\) (tính chất tam giác cân).
=> \(\widehat{ABC}=\widehat{ACB}=\frac{180^0-\widehat{A}}{2}\)
=> \(\widehat{ABC}=\widehat{ACB}=\frac{180^0-50^0}{2}=\frac{130^0}{2}=65^0.\)
=> \(\widehat{ABC}=\widehat{ACB}=65^0.\)
b) Xét \(\Delta ADE\) có:
\(AD=AE\left(gt\right)\)
=> \(\widehat{ADE}=\widehat{AED}=\frac{180^0-\widehat{A}}{2}.\)
Mà \(\widehat{ABC}=\widehat{ACB}=\frac{180^0-\widehat{A}}{2}\left(cmt\right)\)
=> \(\widehat{ADE}=\widehat{ABC}.\)
