Pythagorean Identities

This page covers Pythagorean identities.

The identity: sin²x + cos²x = 1 can be used to derive two more important identities:

By dividing each of these terms by sin²x, we can derive a second identity:

  • 1 + cot²x = cosec²x

By dividing (*) by cos²x, we arrive at the third (and final) identity:

  • tan²x + 1 = sec²x

These identities work for any angle x (measure in either degrees or radians).