I have this solved example, but I need more details. Step by step, please. Book: Mathematical Methods in the Physical Sciences, p. 411.
Example 2. Solve the differential equation:
(5.19)
y - 6y + 9y = 0
We can write the equation as:
(5.20)
D^2 - 6D + 9y = 0
or
D^2 - 3D - 3y = 0
Since the roots of the auxiliary equation are equal, we know that the solution is of the form 5.15, and we simply write the result:
(5.21)
y = Ax + Be^(3x)