Đáp án:
$\begin{array}{l}
Trong:\Delta ABC:\\
\widehat A + \widehat B + \widehat C = {180^0}\\
\Rightarrow \widehat B + \widehat C = {180^0} - \widehat A = {80^0}\\
Do:\widehat B - \widehat C = {20^0}\\
\Rightarrow \left\{ \begin{array}{l}
\widehat B = \dfrac{{{{80}^0} + {{20}^0}}}{2} = {50^0}\\
\widehat C = {80^0} - {50^0} = {30^0}
\end{array} \right.\\
Vậy\,\widehat B = {50^0};\widehat C = {30^0}
\end{array}$
