Sec(a-b) = cos(a+b) / cos^2a - sin^2b I'm trying to prove this, by turning the left side into the right. I am stuck. Presumably you have already done the sum and difference formulas for sin and cos.

In 2022, two high school students created a trigonometric proof of the Pythagorean Theorem—something that’s only ever been accomplished by a few professional mathematicians. Now, a new article not ...