Đáp án:
$\begin{array}{l}
a)\left\{ \begin{array}{l}
m \bot CE\\
n \bot CE
\end{array} \right. \Leftrightarrow m//n\left( {theo\,t/c} \right)\\
\text{Vậy}\,m//n\\
b)m//n\\
\Leftrightarrow \widehat {mAB} + \widehat {ABn} = {180^0}\left( {\text{trong cùng phía}} \right)\\
\Leftrightarrow \widehat {ABn} = {180^0} - {115^0} = {65^0}\\
\text{Vậy}\,\widehat {ABn} = {65^0}\\
c)Do:m//n\\
\Leftrightarrow \widehat {mAB} = \widehat {ABE} = {115^0}\left( {so\,le\,trong} \right)
\end{array}$
