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).
This video explains how to work out phytagoras theorem