Given a rotation matrix R=(cosθ−sinθsinθcosθ)R = \begin{pmatrix} \cos \theta & -\sin \theta \\ \sin \theta & \cos \theta \end{pmatrix}R=(cosθsinθ−sinθcosθ), what is the trace of the matrix?
2cosθ2 \cos \theta2cosθ
000
111
cos2θ\cos^2 \thetacos2θ