# how do I do this trig addition formula problem?

• April 1st 2009, 02:02 PM
RaphaelB30
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
• April 1st 2009, 02:27 PM
skeeter
Quote:

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 ... $\cos(2x) = 2\cos^2{x} - 1$