Trigonometry
Write the following expression in terms of θ\thetaθ only. Use the identity for the cosine of a difference.
cos(θ−90∘)\cos\left(\theta-90^{\circ}\right)cos(θ−90∘)
sinθ\sin\thetasinθ
−sinθ-\sin\theta−sinθ
2cosθ2\cos\theta2cosθ
cos2θ\cos2\thetacos2θ