Trigonometry/More About Addition Formulas

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Related FormulaeEdit

Tangent FormulaeEdit

In the last row of expressions, if then the trigonometric functions are all positive so the positive sign is needed before the square root.

DerivationsEdit

Using cofunctions we know that . Use the formula for and cofunctions we can write


Having derived we replace with and use the fact that cosine is even and sine is odd.

Related FormulaeEdit

DerivationsEdit

Using and the fact that cosine is even and sine is odd, we have