2. Có $\left\{ \begin{array}{l} 3\widehat{A}=4\widehat{B}\\ \widehat{A}-\widehat{B}=20^0 \end{array} \right.$$\Rightarrow \left\{ \begin{array}{l} \widehat{A}=80^0\\ \widehat{B}=60^0 \end{array} \right.$$\Rightarrow \widehat{C}=180^0-\widehat{A}-\widehat{B}=40^0$
2. Có $\left\{ \begin{array}{l} 3\widehat{A}=4\widehat{B}\\ \widehat{A}-\widehat{B}=20^0 \end{array} \right.$$\Rightarrow \left\{ \begin{array}{l} \widehat{A}=80^0\\ \widehat{B}=60^0 \end{array} \right.$$\Rightarrow \widehat{C}=180^0-\widehat{A}-\widehat{B}=40^0$
2. Có $\left\{ \begin{array}{l} 3\widehat{A}=4\widehat{B}\\ \widehat{A}-\widehat{B}=20^0 \end{array} \right.$$\Rightarrow \left\{ \begin{array}{l} \widehat{A}=80^0\\ \widehat{B}=60^0 \end{array} \right.$$\Rightarrow \widehat{C}=180^0-\widehat{A}-\widehat{B}=40^0$