Trigonometry/More About Addition Formulas

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Related Formulae[edit | edit source]

Tangent Formulae[edit | edit source]

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

Derivations[edit | edit source]

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 Formulae[edit | edit source]

Derivations[edit | edit source]

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