I have been stuck on this proof for a while, i know all the identities and think i am either really close and cant see it or my algebra is wrong.

(1-tan^2x)/(1+tan^2x)=1-2sin^2x

i have tried it from many angles, so far the only thing i am sure i did correct was

numerator: (sin^2+cos^2)-(sin^2/cos^2)

denominator: (sin^2+cos^2)+(sin^2/cos^2)(Headbang)

Thanks for any help in advance.