1. The problem statement, all variables and given/known data Prove Rθ+φ =Rθ+Rφ Where Rθ is equal to the 2x2 rotational matrix [cos(θ) sin(θ), -sin(θ) cos(θ)] 2. Relevant equations I am having a hard time trying figure our what is being asked. My question is can anyone put this into words? I am having trouble understanding what the phi may mean? 3. The attempt at a solution I tried to solve this graphical by plotting x and y vectors doing a rotation and plotting those and taking the product of the two rotations or x and y and finding the rotation of x+y. I don't think this is even on the right track and there must be a much simpler way to do this than graphically.