Trigonometry identities

## Contents

* 1 Pythagorean identities
* 2 Law of sines
* 3 Law of cosines
* 4 Sum and difference identities
* 5 Double-angle identities
* 6 Half-angle identities
* 7 Law of tangents

## Pythagorean identities[edit]

## Law of sines[edit]

The law of sines for an arbitrary triangle states:

or equivalently:

## Law of cosines[edit]

The law of cosines (also known as the cosine formula) is an extension of the Pythagorean theorem to arbitrary triangles:

or equivalently:

## Sum and difference identities[edit]

## Double-angle identities[edit]

## Half-angle identities[edit]

Note that  are correct, it means it may be either one, depending on the value of A/2.

## Law of tangents[edit]

The law of tangents: