Pythagorean identity

The Pythagorean identity rephrases the classic Pythagorean theorem in terms of trigonometric functions.

The identity is

$${\sin }^2\theta +{\cos }^2\theta =1.$$

Other variations of the Pythagorean identity include

• ${\tan }^2\theta +1={\sec }^2\theta$,

• and $1+{\cot }^2\theta ={\csc }^2\theta$.