Video: Defining the Pythagorean Identities
Consider the identity sin² 𝜃 + cos² 𝜃 = 1. We can use this to derive two new identities. First, divide both sides of the identity by sin² 𝜃 to find an identity in terms of cot 𝜃 and cosec 𝜃. And divide both sides of the identity through by cos² 𝜃 to find an identity in terms of tan 𝜃 and sec 𝜃.