The following identities, known as the **harmonic identities**, are very useful in solving certain types of trig. equation.

Try and learn them. However, it is a good exercise to try and prove them.

They are all very similar in the method of proof and are based on the addition identities.

I would encourage you to look at how I have proved one and then try the others as they are all very similar.

### The Harmonic Identities:

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