Consider the integral $\int \sin x \cos x d x$
(a) Solve this integral by using $u$ -substitution with $u=$ $\sin x$ and $d u=\cos x d x$
(b) Solve the integral another way, using $u$ -substitution with $u=\cos x$ and $d u=-\sin x d x$
(c) How must your two answers be related? Use algebra to prove this relationship.