The integral is .

(a)

Let ,

.

Consider .

Substitute the corresponding values in the integral.

.

Trigonometric identity: .

.

.

Draw a triangle from the trigonometric substitution.

From the figure, . 

.

(b).

The limits obtained by the trigonometric substitution are

if .

When .

.

(a)

By the integration limits :

.

(b)

By the limits obtained by the trigonometric substitution:

.