Пошаговое объяснение:
sin(a) - cos(a) = 2tg(a/2) / [1 + tg^2(a/2)] - [1 - tg^2(a/2)] / [1 + tg^2(a/2)] = (1 + tg(a/2))^2 / (1 + tg^2(a/2)) = 1.4
