## anonymous one year ago rewrite cos 3x with only sinx and cosx

1. welshfella

Hint:- cos 3x = cos (2x + x)

2. welshfella

use the identity cos (a + b) = cos a cos b - sin a sin b

3. welshfella

put a = 2x and b = x

4. welshfella

i'll start it off for you cos 3x = cos (2x + x) = cos 2x cos x - can you finish it off?

5. anonymous

$\cos (A \pm B)=cosAcosB \mp\ sinAsinB$