Need help solving a differential equation


by Planefreak
Tags: differential, equation, solving
Planefreak
Planefreak is offline
#1
Apr26-09, 08:04 PM
P: 10
1. The problem statement, all variables and given/known data

xy' - (x+1)y = 0, y(0) = 5

2. Relevant equations

Well all of the differential equation stuff seems relevant to me. But from the beginning dy/dx + P(x)y = Q(x) and yeintegral(P(x)dx) = integral(Q(x)eintegral(P(x)dx)dx + C. The separation of variables M(x)dx + N(y)dy = 0.

3. The attempt at a solution

Well I tried following separating everything out: xy' - (x+1)y = 0 y' - ((x+1)/x)y = 0/x then p(x) = -(x+1)/x and eintegral(P(x)dx) = e-integral((x+1)/x dx) and using some more math we end up with e-x/x and that is where I fall apart. Do I integrate this new function and then what? I come up with x/e-x for y and (x-1)ex for y' but when I put it back into the original equation i get x2 + x = x2 -x. Where did I go wrong?
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eok20
eok20 is offline
#2
Apr26-09, 11:59 PM
P: 201
Be careful...you're dividing by x but the initial condition is for x=0. You need to consider the function on an open interval about x=0 and so you cannot divide by x.


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