# Math Help - how do I do this trig addition formula problem?

1. ## how do I do this trig addition formula problem?

I have a list of a bunch of addition properties
Here's the problem. Thanks for your help.

2 cos²10°-1

2. Originally Posted by RaphaelB30
I have a list of a bunch of addition properties
Here's the problem. Thanks for your help.

2 cos²10°-1
note the double angle identity ... $\cos(2x) = 2\cos^2{x} - 1$