As we know that 1+cos 2x = 2sin² x

As, π/2 < x < π

∴ sin x will be positive.

Let Z =

⇒ Z =

⇒ Z = { as we need to consider positive square root}

∵ sin x is positive

∴ Z =

We know that differentiation of sin x is cos x

Hence,

Z = cos x