# Identity Index in Trigonometry

Here is the formula index in trigonometric identities. Again, identities are the fundamentals of trigonometry. This is the counterpart of four basic operations in arithmetic.

**Basic Identity**

**Pythagorean Identity**

**Addition and Subtraction Identify**

**Special Reduction Identity**

**Double Angle Identity**

**Half Angle Identity**

**Product to Sum Identity**

**Sum to Product Identity**

If you want to add more, feel free to add in comment box and I’m glad to include that.

### Dan

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