化简sin²(a-π/2)/cos(a-3π)sin(3π/2+a).

化简sin²(a-π/2)/cos(a-3π)sin(3π/2+a).
化简sin²(a-π/2)/cos(a-3π)sin(3π/2+a)
.

化简sin²(a-π/2)/cos(a-3π)sin(3π/2+a).
sin²(a-π/2)=cos²a
cos(a-3π)*sin(3π/2+a)=-cosa * (-cosa)=cos²a
所以sin²(a-π/2)/cos(a-3π)sin(3π/2+a)=1