Pre-calculus/trig

cos(2x) = cos^2(x) - sin^2(x) = 2 cos^2(x) - 1 = 1 - 2 sin^2(x) No math guniousity used...I just looked it up.

So, is it the first and third option?

Yes....of the 4 options it is the 1st and 3rd.