1. The problem statement, all variables and given/known data 2. Relevant equations ml2/12 3. The attempt at a solution So according to my databook: The axis x'-x' in the question corresponds to axis ZZ in the databook image above. That means in terms of radius, the moment of inertia about axis x'-x' is mr2/2. So in light of this, why is the constant outside the matrix ml2/12? Why not mr2/2?