What is the Pythagorean identity?

The Pythagorean identity is sin2Ø + cos2Ø = 1. This is called the fundamental identity in trigonometry. Two other identities are 1+ tan2Ø = sec2Ø and 1+ cot2Ø = cosec2Ø.

These identities are called Pythagorean identities as they are based on the Pythagorean theorem developed by the Greek mathematician Pythagoras. This theorem has to do with right triangles, and it is applied in trigonometry. Trigonometry was originally developed for making calculations based on the use of the Pythagorean theorem.

These identities were arrived at using the unit circle. A unit circle is a circle having one unit as its radius. A right triangle is formed within this unit circle to arrive at the Pythagorean identities.