This important identity can be derived as a direct result of Pythagoras's theorem, when applied to angles in trigonometry:

sin²x + cos²x = 1 (1)

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

1 + cot²x = cosec²x

By dividing (1) by cos²x, we arrive at the third (and final) identity:

tan²x + 1 = sec²x