Trigonometry/More About Addition Formulas

From Wikibooks, open books for an open world
< Trigonometry
Jump to: navigation, search

Related Formulae[edit]

Tangent Formulae[edit]

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]

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]

Derivations[edit]

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