Let f(x) =

f(– x) = f(x)

And thus f(x) is an even function.

So,

Let cos x = t

Differentiating both sides we get,

– Sinx dx = dt

– √(1 – t²) dx = dt

Limits will also change,

At x = 0, t = 1 and at x = π/2, t = 0

Now the Expression becomes,