How do I use the product rule for derivatives?

Imagine a function f(x)=g(x)*h(x)    [that is, two functions multiplied together]

To find the derivative, f'(x)=g'(x)*h(x) + g(x)*h'(x)    

For example, f(x) = (3x²)*(cos x )        [g(x)=3x²  , h(x)=cosx]

f'(x) = (6x)(cos x ) + (3x²)(-sin x )

        =6xcos(x) - 3x²sin(x)