Problem 1350 (difficulty: 5/10)

Prove Steiner's theorem: if a rigid body has mass \(\displaystyle m\) and its moment of inertia about an axis \(\displaystyle l\) through its center of mass is \(\displaystyle I\), then the moment of inertia about an axis parallel to \(\displaystyle l\) and of distance \(\displaystyle r\) is \(\displaystyle I+mr^2\).

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