Выражение cosα*tgα-2sinα tg(-α)*cosα+sinα

Решение дано на фото.

1) cos(a)*tg(a)-2sin(a) =cos(a) *sin(a)/cos(a) -2sin(a) = sin(a) - 2sin(a) = -sin(a)
2) tg(-a)*cos(a) + sin(a) = -tg(a)*cos(a) + sin(a) = -sin(a)*cos(a) / cos(a) + sin(a) = -sin(a) + sin(a)= 0