Упростите выражение sin(α -π)·cos(3π2+α)-ctg(α-π)·sin(π2+α)·cos(π2−α)

Question

Упростите выражение sin(α -π)·cos(3π2+α)-ctg(α-π)·sin(π2+α)·cos(π2−α)

Answer 1

=-sin a•sin a-ctg a•cos a•sin a=-sin^2a-cos^2a=-(sin^2a+cos^2a)=-1