Use the following Properties:
1. Quotient Property:
tan x = sinx /cos x
2. Pythagorean Property:
cos^2x + sin^2 x =1
3. Double Argument Property
cos 2x = cos^2x-sin^2 x
LEFT HAND SIDE:
(1-tan^2(x/2))/(1+tan^2(x/2)) = (1-sin^2(x/2)/cos^2(x/2))/(1+sin^2(x/2)/cos^2(x/2))
=((cos^2(x/2)-sin^2(x/2))/cos^2(x/2))/((cos^2(x/2)+sin^2(x/2))/cos^2(x/2))
=(cos^2 (x/2)-sin^2(x/2))/(cos^2(x/2))*(cos^2(x/2))/(cos^2(x/2)+sin^2(x/2)
=(cos^2 (x/2)-sin^2(x/2))/cancel(cos^2(x/2))*cancel(cos^2(x/2))/(cos^2(x/2)+sin^2(x/2)
=(cos^2 (x/2)-sin^2(x/2))/(cos^2(x/2)+sin^2(x/2)
=(cos2(x/2))/1
=(coscancel2(x/cancel2))/1
= cos x
:.= RIGHT HAND SIDE