The solution for the differential equation $\dfrac{d^2x}{dt^2}=-9x,$ with initial conditions $x(0)=1$ and $\dfrac{dx}{dt}\bigg \vert_{t=0}=1$ , is

1. $t^2+t+1 \\$
2. $\sin 3t+\dfrac{1}{3}\cos3t+\dfrac{2}{3} \\$
3. $\dfrac{1}{3}\sin3t+\cos 3t \\$
4. $\cos 3t+t$