For the answer to the question above,
Let's work with the left-hand side
We're going to times cosx/1-sinx by 1+sinx/1+sinx, you can do this because 1+sinx/1+sinx is equal to 1, so you aren't really changing anything.
After you've times the top and bottom by 1+sinx, you get:
cosx(1+sinx) / (1-sinx)(1+sinx)
The denominator is a difference of squares, so you get 1-sin^2 x
what you have now is
cosx(1+sinx) / 1-sin^2x
You know that 1-sin^2x is equal to cos^2x
so know you have
cosx(1+sinx) / cos^2x
get rid of the cosx on top by simplifying and the cos^2x so that you're left with
(1+sinx) / cos x
Therefore cosx / 1- sinx = 1 + sinx / cos x
