Find the general solution to the homogeneous differential equation $$\frac{d^2y}{dt^2} + 9\frac{dy}{dt} + 18y = 0$$
The solution can be written in the form $$y = C_1 e^{r_1t} + C_2 e^{r_2t}$$ with $$r_1 < r_2$$ Using this form, $r_1 =$ and $r_2 =$