What is 1-cosx Equal To?

A trigonometric identity!

1 – cos(x) is equal to 2 * sin^2(x/2)

This is known as the “half-angle formula” for cosine.

Here’s the derivation:

1 – cos(x) = 1 – (1 – 2 * sin^2(x/2)) (using the half-angle formula for cosine)
= 2 * sin^2(x/2)

So, 1 – cos(x) is equal to 2 * sin^2(x/2).