$\displaystyle \frac{1-2cos^2{y}}{1-2cos{y} \times sin{y}} = \frac{sin{y} + cos{y}}{sin{y} - cos{y}}$

Could someone give me a pointer? I've been banging my head against this problem for over an hour. I can't seem to find a way to simplify the left hand side.

Thanks for your help,