((1-tan^2(t))/(1+tan^2(t)))=2*cos^2(t)-1 verify the identitiy

Start by substituting tan t = sin t/ cos t
we get (cos^2(t) - sin^2(t)) / (cos^2(t) + sin^2(t))
sin^2(t) + cos^2 (t) = 1
solve it, you'll get the answer.