Initial value problem, end of problem Q

csc2iffy
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Homework Statement


Solve the I.V.P. x2(dy/dx) = (4x2-x-2)/((x+1)(y+1)) , y(1)=1


Homework Equations





The Attempt at a Solution


So far, I got to this:
y2/2 + y = log(x) + 2/x + 3log(x+1) + C
I used the initial conditions to solve for C and got:
C = -1/2 - 3log(2)
Substituting C back in:
y2/2 + y = log(x) + 2/x + 3log(x+1) + (-1/2 - 3log(2))
Now my question is, is it possible to solve for y or is this as far as I can go with the problem?
 
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csc2iffy said:
y2/2 + y = log(x) + 2/x + 3log(x+1) + (-1/2 - 3log(2))
Now my question is, is it possible to solve for y or is this as far as I can go with the problem?

Well it is a quadratic, not the nicest one but you can solve it for y.
 
How do I set it up as a quadratic? I'm getting a little lost with all of the variables
 
csc2iffy said:
How do I set it up as a quadratic? I'm getting a little lost with all of the variables

y^2 + 2y -2[\frac{2}{x} + \ln(x(x+1)^3)] = 0

\text{Then quadratic formula } y = \frac{-2\pm\sqrt{4 - 4(1)(-2[\frac{2}{x} + \ln(x(x+1)^3)])}}{2(1)}

It's horrible, but it'll give you values of y.
 
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could i just complete the square to get:
y = +/- √[2(log(x) + (2/x) + 3log(x+1) + C) + 1] - 1
?
 
Bread18 said:
y^2 + 2y -2[\frac{2}{x} + \ln(x(x+1)^3)] = 0

\text{Then quadratic formula } y = \frac{-2\pm\sqrt{4 - 4(1)(-2[\frac{2}{x} + \ln(x(x+1)^3)])}}{2(1)}

It's horrible, but it'll give you values of y.

Oops forgot the + C, but you get the idea.

csc2iffy said:
could i just complete the square to get:
y = +/- √[2(log(x) + (2/x) + 3log(x+1) + C) + 1] - 1
?

Completing the square would probably be a lot harder, but it should work.
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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