One of the joys of getting old is that you forget things. So one of the things I recall is that the converse of the Pythagorean Theorem is true, that is, if a triangle with short sides *a* and *b* and long side *c* is such that

*a*^{2} + *b*^{2} = *c*^{2},

then the triangle must be a right triangle with the angle between sides *a* and *b* being 90°. But I didn’t recall how to prove it. So I thought I would see if I could do it without looking up any sources.

See the Pythagorean Theorem Converse