Hi could I get Help with this question really struggling I need to use angle formula to show cos^2x=1/2 (cos2x-1).
Which "angle formula" are you supposed to use? Are you talking about the double angle formula for cosine?
$\displaystyle \cos(2x) = 2\cos^2 x -1$
Is that the "angle formula" you are referring to? If it is, then add 1 to both sides. Then divide both sides by 2.