- #1
ElijahRockers
Gold Member
- 270
- 10
Homework Statement
Find two linearly independent power series solutions about the ordinary point x=0 for
y'' + x2y' +y =0
The Attempt at a Solution
Alright so we are supposed to try
y(x) = Ʃ∞n=0 {Cn(x-x0)n} [but x0=0 so i won't include it in the derivatives]
so y'(x) = Ʃ∞n=1 {nCnxn-1}
and y''(x) = Ʃ∞n=2 {n(n-1)Cnxn-2}
Shifting indices and taking out terms to make the exponents of x and the starting points of the series equal (and then finally adding the series):
C0 + 2C2 + Ʃ∞n=1 [(n+2)(n+1)Cn+2 + (n-1)Cn-1 + Cn]xn = 0
To me, this would mean that C0 and C2 both equal 0 right?
Then also That whole jumble inside the final series (except for the xn) also must equal zero...
I guess I am lost at this point. The teacher did it differently. He starts the final series at n=2 instead of n=1. Shouldn't it still be possible to do it my way?
I have attached his solution for reference.
Thanks for the help, final exam is on monday, wish me luck! Diff Eq in 5 weeks has been pretty rough on me...
EDIT: I forgot to mention... I am not quite sure how to arrive at two different solutions... it seems to me that in my notes the teacher factored something out and somehow got two solutions but I am pretty confused as to what is going on there.