Question

cos10X+cos12X=0 x=?

Answer 1

http://en.wikipedia.org/wiki/Trig_identity#Product-to-sum_and_sum-to-product_identities
use these identities
\[\cos(11x)\cos x = \frac{\cos(11x-x) + \cos(11x+x)}{2}\]

Answer 2

ohh thx man for your time! helps a lot!

Answer 3

yw

Answer 4

but the identiti is X and i need +

Answer 5

it doesnt matter, the "+" is just in right side

Answer 6

lets try the other one
look at "sum to product"
\[\cos(10x) + \cos(12x) = 2\cos(\frac{10x+12x}{2}) \cos(\frac{12x-10x}{2})\]

Answer 7

yes man i understand.. thx again (: