Draw a right triangle where the hypotenuse is 1 and one of the acute angles is x. Label the hypotenuse H, the side opposite x as O and the third side as A (for adjacent)
Here are the definitions of sin and cosine:
sin(x) = O/H
cos(x) = A/H
Pythagorean Theorem: O² + A² = H²
Divide both sides by H²
and substitute the above definitions.
Solution
