Trigonometry/Trigonometric identities< Trigonometry
|Please share your thoughts about whether to keep this page at Wikibooks.
Maintain this notice so this page can receive a fair review and people have time to boldly address reasonable concerns through concrete improvements. Remove or replace this notice after discussion concludes and a community decision is made. Please also consider notifying the primary contributors on their discussion page with
What is an identity?Edit
An identity is an equation that holds true for all values of the variables appearing in it, because it either is a definition or is the logical consequence of a definition. An example of a definitional identity is An example of an identity that can logically be proven to hold for all values of its variable is the Pythagorean identity expressed in trigonometric form: