Given that

Let x=-cosθ ⇒ θ=cos^-1(-x).

Using and , we get

Differentiating with respect to x, we get

–(1)

Since, x=-cosθ ⇒ or -(2)

Also, since θ=cos^-1(-x), therefore –(3)e

Substituting (2) and (3) in (1), we get