Algorithm: General Solution (Homogeneous Version)
1. Find the characteristic equation.
2. Find the roots to the characteristic equation.
2.1 If r is a real root of multiplicity k, then
e rx , xe rx , . . . , x k−1 e rx
are k linearly independent solutions to the ODE.
2.2 If r = a + bi is a complex root of multiplicity k (r = a − bi is
also a complex root of multiplicity k), then
e ax sin(bx), xe ax sin(bx), . . . , x k−1 e ax sin(bx)
e ax cos(bx), xe ax cos(bx), . . . , x k−1 e ax cos(bx)
are 2k linearly independent solutions to the ODE.
3. Finally, y (x) is a linear combination of your solutions. Example
Find the general solution to the ODE.
y (6) + y (4) = 0 Example
Suppose the characteristic equation to a homogeneous linear ODE
with constant coefficients is given by
r 2 (r + 1)3 (r 2 − 2r + 2)2 = 0.
Find the general solution to the ODE. Example
Suppose the roots and multiplicities to the characteristic equation
of some homogeneous linear ODE with constant coefficients is
given below.
r1 = 2, k1 = 3
r2 = 2 + i, k2 = 1
r3 = 2 − i, k3 = 1
r4 = 2i, k4 = 2
r5 = −2i, k5 = 2
Find the general solution to the ODE.
Higher-order Homogeneous Linear ODEs
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