Question

a[cosA + cos(A+C)] is supposed to become 2acos(c/2)cos[A+(C/2)]. How?

Answer 1

Do you know the trigonometric formula of type -
cos(A) + cos(B) = 2cos(...)cos(...)
??

Answer 2

Yes, but that'll give give me A+C whole divided by 2 on the second term in the RHS.

Answer 3

Nope..try to do it again

Answer 4

Oh, right. Got it :P Thanks ! :)

Answer 5

Was :P necessary ?? :P

Answer 6

The formula, yes :P

Answer 7

XD