Where θ is the lowercase Greek letter theta when you enter the expression 2cos2 (θ) - 1?

The problem ask to find the theta of the expression 2cos2 (0) - 1. So to calculate that, you must first follow the theory and the following the rule of the trigonometric function and expression, so base on that, the value of theta would be cos2theta. I hope you are satisfied with my answer and feel free to ask for more