How do you make one side equal to the other side?

(secx/secx-tanx)=sec^2x+secxtanx

LS:

sec/(sec-tan)
multiply by (sec+tan) top and bottom
sec(sec+tan) / (sec^2-tan^2)
now recall that sec^2 = 1+tan^2, so we have
(sec^2 + sec tan) / 1
sec^2 + sec tan
= RS