3 Identities 3.1 Basic Trigonometric Identities So far we know a few relations between the trigonometric functions. For example, we know the reciprocal relations: 1. csc θ = 1 sin θ when sin θ n=0 2. sec θ = 1 cos θ when cos θ n=0 3. cot θ = 1 tan θ when tan θ is de±ned and not 0 4. sin θ = 1 csc θ when csc θ is de±ned and not 0 5. cos θ = 1 sec θ when sec θ is de±ned and not 0 6. tan θ = 1 cot θ when cot θ is de±ned and not 0 Notice that each of these equations is true for all angles θ for which both sides of the equa-tion are de±ned. Such equations are called identities , and in this section we will discuss several trigonometric identities
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