What is a double angle identity to find the exact value of cos?
Group of answer choices

cos⁡(2a)=〖cos〗^2⁡(a)+〖sin〗^2⁡(a)

cos⁡(2a)=〖cos〗^2⁡(a)

cos⁡(2a)=2 〖cos〗^2⁡(a)-1

cos⁡(2a)=〖2cos〗^2⁡(a)-2 〖sin〗^2⁡(a)