If, show that f(tanθ) = sin2θ.
Given
We need to prove that f(tanθ) = sin2θ.
We have
We know
However, cos2θ + sin2θ = 1
⇒ f(tanθ) = 2sinθcosθ
∴ f(tanθ) = sin2θ
Thus, f(tanθ) = sin2θ