The trigonometric identities are a set of equations derived from the properties of the circle and the trigonometric functions. The identities are useful when manipulating and transforming expressions.
| Name | Identity |
|---|---|
| Tangent Identity | |
| Cotangent Identity | |
| Pythagorean’s Identity | |
| Sum of Two Angles (Sine) | |
| Sum of Two Angles (Cosine) | |
| Difference of Two Angles (Sine) | |
| Difference of Two Angles (Cosine) | |
| Double-Angle Identity (Sine) | |
| Double-Angle Identity (Cosine) | |
| Double-Angle Identity (Cosine 2) | |
| Double-Angle Identity (Cosine 3) | |
| Half-Angle Identity (Cosine) | |
| Half-Angle Identity (Sine) |
The trig identities can be derived using the strategies outlined on these pages: