# 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

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