Question

Hi,
If cos(a+b)=cosacosb-sinasinb and
if cos(a- b)=cosacosb+sinasinb then cosacosb=?

Answer 1

I think the answer is like 1/2[something] but I dont know where to start!

Answer 2

Has to do with trig formulas but I need some help.

Answer 3

so if cos(a+b)=cosacosb -sinasinb
and cos(a-b)=cosacosb +sinasinb so than if you assum these will get
------------------
cos(a+b +cos(a-b)=2cosacosb and now just divide both sides by 2 and will get

cos(a+b)+cos(a-b)
----------------- = cosacosb
2

hope so much that is understandably sure rigth

good luck

bye