**Theorem of Parallel Axes**

We have to obtain the moment of inertia of a body with mass M and with the centre of mass at C about a given line AB. Visualise a line CZ parallel to AB through C.

Let I

_{0}be the moment of inertia of the body about CZ respectively.

If the perpendicular distance between AB and CZ is d

Then I, the moment of inertia of the body about AB is going to be

I = I

_{0}+ Md²

**Theorem of Perpendicular axes**

This theorem is applicable only to the plane bodies. Let X and Y axes be chosen in the plane of the body and Z=axis perpendicular to this plane, and the three axes are mutually perpendicular.

Ix, Iy, Iz are moment of inertia of the body about x,y, and z-axes respectively.

According to the theorem

Iz = Ix + Iy

(Chapter: Rotational Mechanics)

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