exp(2jt) => texp(-2jt)
exp(-2jt) =>texp(2jt)
use Eulers Identity
cos(2t) = .5exp(2t) + .5exp(-2t) => t(.5)exp(-2t) + t(.5)exp(2t) =>t(.5exp(2t) + .5exp(-2t)) => tcos(2t)
