The general solution to the second-order differential equation $\displaystyle y'' + 6 y' - 16 y = 0$ is in the form $\displaystyle y(x) = c_1 e^{r_1 x} + c_2 e^{r_2 x}.$ Find the values of $r_1$ and $r_2.$

Answer: $r_1 =$ and $r_2 =$