RU-ALLRUSSIAN 1983 Problem 8

A and B are acute angles such that $\sin^{2} \mathrm{A} + \sin^{2} \mathrm{B} = \sin (\mathrm{A} + \mathrm{B})$ . Show that $\mathrm{A} + \mathrm{B} = \pi / 2$ .