Write a val

We know that cos²x = 1 – sin²x

(a²sin²x + b²cos²x) = a²sin²x + b²(1 – sin²x)

= (a² – b²)sin²x + b²

Let, sin²x = t

Differentiating both sides with respect to x

= sin 2x

⇒ dt = sin2x dx

Use formula

Again, put t = sin²x