Cos 2x =

check all that apply.

  see below

Step-by-step explanation:

The double angle formulas for trig functions are generally based on the sum of angle formulas, where the two angles are equal.

  cos(a+b) = cos(a)cos(b) -sin(a)sin(b)

When a=b=x, then ...

  cos(2x) = cos(x)² -sin(x)²

The Pythagorean identity can be used to substitute for either of the squares:

  cos(2x) = (1 -sin(x)²) -sin(x)²

  cos(2x) = 1 - 2sin(x)²

or

  cos(2x) = cos(x)² -(1 -cos(x)²)

  cos(2x) = 2cos(x)² - 1

1/4 because there is 4 grades.