# Proving Trigonometric Identities

1. Aug 8, 2010

### snowpanda

1. The problem statement, all variables and given/known data

Prove (using the left side):

sinΘ tanΘ = cosΘ sec^2Θ - cosΘ

2. Relevant equations

3. The attempt at a solution

2. Aug 8, 2010

### HallsofIvy

Staff Emeritus
$$sin(\theta)tan(\theta)= \frac{sin(\theta)}{cos(\theta)}tan(\theta)cos(\theta)= \tan^2(\theta)cos(\theta)$$

Now use the fact that $tan^2(\theta)= sec^2(\theta)- 1$.