What is the trigonometric identity used to simplify this expression?

1. Mar 23, 2012

cocopops12

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

2. Mar 23, 2012

Office_Shredder

Staff Emeritus
It's not a trig identity

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