Mathematics
Fundamental Trigonometric Identity
The most important Pythagorean identity.
sin²θ + cos²θ = 1
Formula Explanation
It follows directly from the definitions of sine and cosine in a unit circle or right triangle.
Variables Explained
θ = any angle where sin and cos are defined.
Solved Example
If sin θ = 3/5, find cos θ.
cos²θ = 1 - 9/25 = 16/25 → cos θ = ±4/5.