# What is a non-geometric proof to prove the sine addition formula?

What is a non-geometric proof to prove the sine addition formula?

I know that method that using euler's constant or taylor's series works, but is there any others?

Search the google with the "non-geometric proof of sine addition formula" only provide me with the geometric way...

How do you define the $\sin$ function ? –  Belgi Oct 1 '12 at 22:05