Linked from

The 3 pages that link to Pythagorean trigonometric identity, each with the reason it gives.

• TangentRelated: Dividing it by cos²(x) yields 1 + tan²(x) = sec²(x).

• Trigonometric substitutionRelated: The identities make radicals such as √(1 − sin²θ) simplify to trigonometric functions.