The process of integration can be made easier by using a method called "Integration by Substitution." This method is used when an integral contains some functions and its derivatives. [ f(8(x))s'(x) dx In the above illustration, g'(x) is the derivative of g (x). Represent g (x) by u and then find du (differential of u). Integrate f()da then replace " by g (x). EXAMPLE I Evaluate (x' + 5) 2xdx. SOLUTION Let u = x +5 du = 2xdx S ( x + 5)' 2xdx = fudu +c x' + 5 +C