Find the general solution of $ y'''- y'' - 9y' +9y = 0 $ Find the general solution of  $ y'''- y'' - 9y' +9y = 0 $
The answer is
$y=c_{1}e^{-3x}+c_{2}e^{3x}+c_{3}e^{x}$
how do i approach this problem?

Try to substitute $e^{\lambda x}$ in the equation and solve the algebraic equation in $\lambda$ as is usually done for second order homogeneous ODEs.
