I don’t understand how to do this!
3 Answers

This is also known as the double angle trig identity which is cos2x=cos^2xsin^2x

cos(2x) = cosÂ²x – sinÂ²x
sinÂ²x + cosÂ² x = 1
sinÂ²x = 1 – cosÂ²x
cos(2x) = 1 – cosÂ²x + cosÂ²x
cos(2x) = 1
x = 0

3x times 4

cos^2(x) – sin^2(x)
It’s called a trigonometric identity.

cos (2x) = cosÂ²x – sinÂ²x = 1 – 2sinÂ²x = 2cosÂ²x – 1