in general we have this identity: $\displaystyle \cos x + \cos y = 2 \cos \left(\frac{x+y}{2} \right) \cos \left(\frac{x-y}{2} \right).$ do you remember? now just put $\displaystyle x=6a$ and $\displaystyle y=2a$ and see what you get!
in general we have this identity: $\displaystyle \cos x + \cos y = 2 \cos \left(\frac{x+y}{2} \right) \cos \left(\frac{x-y}{2} \right).$ do you remember?
No. I gotta teach myself a lot of the maths I haven't come across this thanks a lot!
are there any more important ones i should be aware of? I have learned compound angle and double angle formulae
Last edited by mr fantastic; May 8th 2009 at 02:07 PM.
Reason: Merged posts