Why is the derivative of F (x) = 2F (2-x) f '(x) = - 2F' (2-x)

Why is the derivative of F (x) = 2F (2-x) f '(x) = - 2F' (2-x)

f(x)=2f(2-x)
f'(x)=[2f(2-x)]'
=2f'(2-x)*(2-x)'
=-2f'(2-x)