Answer:

Explanation:
we would like to solve the following using double-angle formula:

there're 4 double Angle formulas of cos function which are given by:

since the question doesn't allude which one we need to utilize utilize so I would like to apply the second one, therefore
step-1: assign variables
to do so rewrite the given function:

so,
Step-2: substitute:

recall unit circle thus cos300 is ½:

simplify square:

reduce fraction:

simplify substraction and hence,
