# Use trig identities to show that

1. Apr 8, 2014

### ivan_x3000

1. The problem statement, all variables and given/known data
use trig identities to show that

(b) cos(tan^(−1)[x])=1/√(1+x^2) for −1/2π<x<1/2π.

2. Relevant equations
i think Pythagoras has to applied but that is geometric reasoning hmm

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Apr 8, 2014

### jbunniii

Maybe try bringing $\sin(\tan^{-1}(x))$ into the picture?

3. Apr 8, 2014

### Dick

tan^(-1)(x) represents an angle whose opposite side is x and whose adjacent side is 1. Use that geometry to figure out the cosine.

4. Apr 8, 2014

### SammyS

Staff Emeritus
cos → sec → tan