For all real numbers x , cos 2x

Answer 1

cos(2x) = cos^2(x) - sin^2(x)

= 2cos^2(x) - 1

= 1 - 2sin^2(x)

all 3 are trig identities which are equal for all real numbers x

(or did you mean cos^2(x)? IF so, then cos^2(x) = 1- sin^2(x), also true for all real numbers x

It's another trig identity