Help with Proving Long Identity?

Question

Show that cos^2(y)sin^2(x)+

sin^2(y)sin^2(x)+

cos^2(y)cos^2(x)+

sin^2(y)cos^2(x) = 1

Answer 1

cos^2(y)sin^2(x) + sin^2(y)sin^2(x) + cos^2(y)cos^2(x) + sin^2(y)cos^2(x)

= (cos^2(y) + sin^2(y)) * (sin^2(x) + cos^2(x))

= 1 * 1

= 1