Differentiate sin(x)cos(x) with respect to x?

You will have to use the Product Rule. The Product rule: when y=f(x)g(x), then dy/dx=f'(x)g(x)+f(x)g'(x). In this example, f(x)=sin(x) and g(x)=cos(x). Hence f'(x)=cos(x) and g'(x)=-sin(x). Using these and subbing into the Product rule, dy/dx=cos²(x)-sin²(x).