For each of the indefinite integrals below, select which of the following trig substitutions would be most helpful in evaluating the integral. Do not evaluate the integrals. A. x=9tanθ B. x=9sinθ C. x=9secθ 1. ∫ 81−x 2
​
x 2
dx
​
2. ∫x 2
81+x 2
​
dx 3. ∫ (81−x 2
) 3/2
dx
​
4. ∫ x 2
−81
​
dx 5. ∫ (81+x 2
) 3
dx
​