- #1
Jim4592
- 49
- 0
Homework Statement
x2y'' + xy' + 4y = 0
Homework Equations
y = xr
y' = r xr-1
y'' = r(r-1)xr-2
The Attempt at a Solution
x2[r(r-1)xr-2] + x [r xr-1] + 4xr = 0
(r2-r)xr + r xr + 4xr = 0
[(r2-r) + r + 4]xr = 0
r2 - r + r + 4 = 0
r2 + 4 = 0
from the quadratic equation i know that: r = 2i and r = -2i
so y = c1x2i + c2x-2i
my question is how can i remove the imaginary number from the answer.
Thanks in advanced!