TRIGONOMETRIC SUBSTITUTION Integrals which contain anyone of the expressions: a2 - u2 a2+ 12 u2 - a2 where a is a positive constant and u = f(x) . Transform the given integral into a trigonometric integral by using the following substitution: 1. If the integrand contains a2 - u, let u = a sin 0. Then du = a cos 0 de. 2. If the integrand contains a +us, let u = a tan 0. Then du = a sec2 0 do. 3. If the integrand contains u - a', let u = a sec 0. Then du = a sec e tan 0 dedx = In + C e2x 4 1 2x + 1