1. Feb 8, 2007

ArjSiv

So it's apparently possible to prove that e^{-iAx} = cos(x)I + isin(x)A given that A^2=I.

What I don't understand is how this is supposed to be derived. Any help would be appreciated as this is driving me nuts and this is probably something that is very easy to prove...

2. Feb 8, 2007

Dr Transport

Ther are two ways, expand the exponential use the eigenvalues and eigenvectors of the matrix A.

3. Feb 8, 2007

ArjSiv

Ahh, I knew I was missing something stupid. I didn't realize that A^{2n}A = A.

Thanks :)