Use trigonometric identities to transform the left side of the equation into the right side (0 < θ < π/2).
sin2 θ − cos2 θ = sin2 θ − (_______)
= 2 sin2 θ − 1
sin2 θ − cos2 θ = sin2 θ − (_______)
= 2 sin2 θ − 1