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