The solution for the differential equation $\frac{d^2x}{dt^2}=-9x$

with initial conditions $x(0)=1$ and $\frac{dx}{dt}|_{t=0}=1$ , is

1. $t^2+t+1$
2. $sin3t+\frac{1}{3}cos3t+\frac{2}{3}$
3. $\frac{1}{3}sin3t+cos3t$
4. $cos3t$+$t$

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