1) I can assume all these matrices to be 2x2. We have matrix A and B and AB = BA, that is, they commute.. Prove if C = A^2 + 2*A and D = A^3 + 5 * I (I is identity matrix), then CD = DC. Then give a theory that generalizes this. 2) why does R(theta)R(phi)=R(theta+phi)? (explain with "simple" words) Knowing this, derive the formulas cos(theta + phi) and sin(theta + phi) in terms or cos(theta),cos(phi),sin(theta), and sin(phi). - I haven't done a proof course yet so I'm completely lost.