How to Derive Euler's Identity?

[DiracPool]

Hello. Please tell me how do I derive:

cos(θ)=1/2 ($e^{iθ}$+$e^{-iθ}$)

from:

$e^{iθ}$=cos(θ) + isin(θ)

as well as:

sin(θ)=1/2i ($e^{iθ}$-$e^{-iθ}$)

I can't figure it out...for example, where does the 1/2 come from? Thank you

 

[DiracPool]

Never mind, I just figured it out by looking at this thread that just happens to be right next to mine: https://www.physicsforums.com/showthread.php?t=597539

Thanks anyway.

 

[pwsnafu]

Write out what $e^{-i\theta}$ is.

Edit: ninja'd by the OP