Sin(90+a)×cos(180+a)/cos2(a-180)×tg(a-270)

Question

Sin(90+a)×cos(180+a)/cos2(a-180)×tg(a-270)

Answer 1

Сosa*(-cosa)/(cos²a*(-tga))=-cos²a/(-cos²a*tga)=1/tga=ctga