why is the sign for the sum and difference formula for cos(u+/-v) = cosucosv-/+sinusinv i.e. the sign is negative instead of positive

Question

anonymous · Answer

like in calulus when you want to find the derivative of cosx using first principle and the identity is cosucosv-sinusinv

anonymous · Answer

Are you familiar with Euler's Formula?
$$e^{i\theta} = \cos(\theta)+isin(\theta)$$
There is a pretty good proof using that fact that im uploading in a sec

anonymous · Answer

Here ya go :)

anonymous · Answer

if theres something i put that isnt clear, feel free to ask so i can clarify :)

anonymous · Answer

no am not familiar with euler's

anonymous · Answer

i dont understand lol...

anonymous · Answer

thanks though joe!

anonymous · Answer

Good luck with that one...the other proof isn't all that great as well.