Question

(sina-cosa)^2 + 2sina cosa

Answer 1

Воспользуемся формулой "квадрат разности"
$(a-b)^2=a^2-2ab+b^2\ (sin alpha -cos alpha )^2 + 2sin alpha cos alpha=\ sin^2 alpha -2sin alpha cos alpha+cos^2 alpha + 2sin alpha cos alpha=sin^2 alpha +cos^2 alpha = 1$