## Calculus (3rd Edition)

(a) $u=x^2+9$. (b) $u=x^3$. (c) $u=\cos x$.
(a) Here, we can use the substitution $u=x^2+9$. (b) Here, we can use the substitution $u=x^3$. (c) Here, we can use the substitution $u=\cos x$.