Line $g$ is given and point $M$, $M \notin g$. Find the image ($\sigma_g$) of a line $a$, $M \in a$ and $a || g$.
I made the diagram by choosing point $P$, $P\in a$ and found the images of $P$ and $M$ - $P_1$ and $M_1$, respectively. These points determine the desired line. I think that $P_1M_1MP$ is а rectangle, but I don't know how to show it. I'd be very grateful if you could help me.
