C-09-Q198mediumsingle_mcqIf cos2θ−sin2θ=12\cos^2\theta - \sin^2\theta = \dfrac{1}{2}cos2θ−sin2θ=21, then cos4θ−sin4θ=?\cos^4\theta - \sin^4\theta = ?cos4θ−sin4θ=?a111b12\dfrac{1}{2}21c