Posted by Jack on Thursday, December 19, 2013 at 3:50pm.
I assume you mean (2-sec^2 x)/(1+tan^2 x) since sec^2 x = 1+tan^2 x, we have (1-tan^2 x)/(sec^2 x) multiply top and bottom by cos^2 x = (cos^2 x - sin^2 x)/1 = cos(2x)