упростить
(sina+cosa)^2+(sina-cosa)^2-2

( sina + cosa)^2 + ( sinа - cosа )^2 - 2 = sin^2a + 2sinacosa + cos^2a + sin^2a - 2sinacosa + cos^2a - 2 = 1 + 2sinacosa + 1 - 2sinacosa + 1 - 2 = 2 - 2 = 0