Đáp án:
$\begin{array}{l}
2)Do:\widehat A + \widehat B + \widehat C + \widehat D = {360^0}\\
\Leftrightarrow \widehat D = {75^0}\\
\Leftrightarrow \left\{ \begin{array}{l}
gn\widehat A = gn\widehat D = {180^0} - \widehat A = {105^0}\\
gn\widehat B = {180^0} - {90^0} = {90^0}\\
gn\widehat C = {180^0} - {120^0} = {60^0}
\end{array} \right.\\
B3)\\
\left\{ \begin{array}{l}
\widehat N = \widehat M + {10^0}\\
\widehat P = \widehat N + {10^0} = \widehat M + {20^0}\\
\widehat Q = \widehat P + {10^0} = \widehat M + {30^0}
\end{array} \right.\\
Do:\widehat M + \widehat N + \widehat P + \widehat Q = {360^0}\\
\Leftrightarrow \widehat M + \widehat M + {10^0} + \widehat M + {20^0} + \widehat M + {30^0} = {360^0}\\
\Leftrightarrow 4\widehat M + {60^0} = {360^0}\\
\Leftrightarrow \widehat M = {75^0}\\
\Leftrightarrow \left\{ \begin{array}{l}
\widehat N = {85^0}\\
\widehat P = {95^0}\\
\widehat Q = {105^0}
\end{array} \right.
\end{array}$
