## Detailed description

Cartesian plane. Points *P*(*x*_{1}, *y*_{1}), *Q*(*x*_{2}, *y*_{2}), M(*x, y*) shown. Point (*x*, *y*_{1}) is labelled *S*, point (*x*_{2}, *y*) is labelled *T*. *M* is the midpoint of drawn segment *PQ*. Segments *PS, SM, MT, *and* TQ* are drawn dotted. Right angles marked at *S* and *T*.