Trigonometric identities
This original textbook reading covers part of the AP topic. Follow the AP course outline for complete topic instruction and practice.
Glossary and deeper reading · 1 refreshers
These editorial refreshers supplement the reading. Definitions and examples are added guidance; original source wording and recorded answers remain in their original context.
-
Trigonometric identity
A trigonometric identity is an equality that holds for every input where both sides are defined. Identities let you rewrite expressions without changing their values on that shared domain. For example, sin²θ+cos²θ=1 follows from the unit circle. Any division used while rewriting an identity can introduce domain restrictions.