The Pythagorean theorem $\text{hyp}^2 = \text{opp}^2 + \text{adj}^2$ leads directly to which trigonometric identity?

Dividing the Pythagorean relation $\text{hyp}^2 = \text{opp}^2 + \text{adj}^2$ by ${}^{}$ converts the sides into and , yielding . This is why it is called a Pythagorean identity.