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... trigonometric identities are equalities that involve trigonometric functions and are true for every single value of the occurring ... The basic relationship between the sine and the cosine is the Pythagorean trigonometric ... One method of proving these identities is to apply Euler's ... - read more

Before we start to prove trigonometric identities, we see where the basic identities come from. Recall the definitions of the reciprocal trigonometric functions, csc θ, sec θ and cot θ from the trigonometric functions chapter: - read more

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