Question on property of integral f(x) limits of 0 and a =int f(a-x) limit 0 and a

Look In the satement :

RHS >Integral f(a-x) with limits of 0 and a, can also be evaluated as F(a-x) with the same limits

so it equal to F (a-x) from 0 and a

The above statemnt is incorrect , because when u integrate f(a-x) , you will get F(a-x)/-1 , u also devide the integral by derivative of the expression a-x , such as integration of cos2x is (sin2x)/2