What is the trigonometric identity used to simplify this expression?

[cocopops12]

Could anyone please tell me how are those two expressions equivalent?! what are the identities used?

 

[Office_Shredder]

It's not a trig identity

\frac{1}{1-\sin z} = \frac{1+\sin z}{1+\sin z} \frac{1}{1-\sin z} = \frac{1+\sin z}{1-\sin^2 z}