Theorem of perpendicular axis
It states that if I_{X}_{X} and I_{Y}_{Y} be the M.I. of plane section about the two mutually perpendicular axes meeting at a point. The M.I. I_{ZZ }which is perpendicular to plane and passing through intersection of X-X and Y-Y can be given by the relation
I_{Z}_{Z} = I_{XX }+ I_{YY}
I_{Z}_{Z} called as Polar moment of inertia also.