Correct answer is B.

Since we are concerned with the area above the x – axis, we’ll be considering the positive root.
We can see that at x = 0, y = 0.
So,

Putting √x = u
We get du = (1/2√x)dx
or, dx = 2u du
So,

Putting u = √2√a sin t
We get du = √2√a cos t dt

