Solve:
\(y'' - \omega^2y = 0, y(0)=1,y'(0)=1\\\text{Assuming }\omega \neq 0 \)
Like so:
\(y=Ae^{\omega x}+Be^{-\omega x}\\ y'=\omega Ae^{\omega x}-\omega Be^{-\omega x}\\ y''= \omega^2y\)
Now use your initial conditions to find A and B.