For the angle *α* shown in Figure B.1, the trigonometric functions are defined as follows.

**Figure B.1. Equation (B.1) defines the trigonometric functions in terms of the angle α shown in this triangle.**

**Equation B.1. **

The relationships among the trigonometric functions listed below follow immediately from the definitions.

**Equation B.2. **

The cosine function is an *even* function, meaning ...

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