(sin^5x*cos^5x)′
=(sin^5x)′cos^5x+sin^5x(cos^5x)′
=5sin^4x*(cosx)*(cos^5x)+sin^5x(5cos^4x)*(-sinx)
=5sin^4xcos^4x[cos^2x-sin^2x]
=10sin^4xcos^4x*(cos2x)