First Order Diffy Q Problem with Bernoulli/Integrating Factors

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Homework Help Overview

The discussion revolves around a first-order differential equation involving Bernoulli's equation and integrating factors. Participants are examining the challenges associated with solving the integral that arises in the process.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to apply Bernoulli's method to linearize the equation and use integrating factors. They express uncertainty about their approach due to encountering an integral that involves the Ei function. Other participants question the formulation of the problem and suggest there may be a typo in the original equation.

Discussion Status

Participants are actively discussing the formulation of the differential equation and exploring potential errors in the original statement. Some guidance has been offered regarding the interpretation of the equation, but no consensus has been reached on the correct approach or solution.

Contextual Notes

There are indications of possible typos in the problem statement, which may affect the interpretation of the differential equation. The complexity of the integral and the use of the Ei function are also noted as points of concern.

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Homework Statement
If dy/dy + y = (1-1/x)(1/(2y)), solve when x=1, y=1/sqrt(2). Hint: Use a substitution to get into the form of a first order differential equation
Relevant Equations
integrating factor = e^integral(P(x))
v=y^(1-n)
dy/dx +P(x)y=Q(x)y^n
I seem to be getting an unsolvable integral here (integral calculator says it's an Ei function, which I've never seen). My thought was to use Bernoulli to make it linear and then integrating factors. Is that wrong? The basic idea is below:

P(x) 1, Q(x) = 1/2(1-1/x), n=-1, so use v=y^1- -1)=y^2

so y=sqrt(v), dy/dx=1/(2sqrt(v))dv/dx

Thus the equation becomes 1/(2sqrt(v))dv/dx + sqrt(v) = 1/sqrt(v) * 1/2(1-1/x))
Multiplying by 2* sqrt(v) gives dv/dx +2 v = (1-1/x)
Use the integrating factor e^2x gives: d/dx(v*e^(2x)) =e^(2x)(1-1/x) = e^(2x) - e^(2x)*1/x
ve^(2x) then just equals the antiderivative of e^(2x) - e^(2x)*1/x, but that second term seems to give a problem. Is my method incorrect? Not sure how to proceed.
 
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I can't spot any mistakes in your solution (except that you got to learn using ##\LaTeX## )so it probably is correct.

I tried wolfram and it also gives the solution in terms of the Ei(2x) function
https://www.wolframalpha.com/input/?i=y'+y=(1-1/x)0.5(1/y)

Maybe check again the exact statement of the problem. There might be some typo after all.
 
Assuming you mean ##\frac{dy}{dx}+y=(1-\frac 1x)(\frac 1{2y})## (you wrote dy/dy), it already is a first order ODE.
This does suggest a typo,
 
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haruspex said:
Assuming you mean ##\frac{dy}{dx}+y=(1-\frac 1x)(\frac 1{2y})## (you wrote dy/dy), it already is a first order ODE.
This does suggest a typo,
I think there he wanted to write first order linear
 
Delta2 said:
I think there he wanted to write first order linear
Yes, that fits. I agree it leads to a nasty integral; I had it in the form of a double exponential.
 

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