# Having hard time with Angular Momentum and Parallel axis theorem

I'm having hard time with Angular Momentum and Parallel axis theorem.

Please explain these 2 formulas. Is one formula derived from the other?

$$J = J_{cm} + R_{cm} \times P_{cm}$$

$$I = I_{cm} + MD^2$$

The first formula is for Angular Momentum and the second one is for the mass moment of inertia. However, I think that the first formula only applies in a specific case. Is this true?

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