2 Homework Problems EXERCISE 13 Evaluate the integral 202 Vac2 + a2using three different substitutions a) :L' = 1 / t, b) a: = a tan t, c) a: = a sinh t. EXERCISE 14 Evaluate the integral [3\" cos a: do: 0 2 + sin 3: using a suitable trigonometric substitution. Comment on the change of metric, that is, on how the interval changes. (Are you comfortable with this result?)