Constructing a second solution

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Homework Help Overview

The discussion revolves around finding a second solution to a differential equation of the form xy" + y' = 0, given a particular solution y1 = ln(x). Participants are exploring the application of a formula for constructing a second solution based on the first.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the use of a specific formula for finding the second solution and question the correctness of the integration steps involved. There is uncertainty about the application of the exponential integral and the manipulation of ln(x) within the integral.

Discussion Status

The discussion is ongoing, with participants raising questions about the validity of the original poster's approach and the assumptions made regarding the integration process. Some guidance has been offered regarding the need for clarity in the steps taken, but no consensus has been reached on the correctness of the solution.

Contextual Notes

There is a noted concern about the triviality of the proposed solution y2 = 1, as it could imply that any constant would satisfy the differential equation. Participants are also addressing potential typos and clarifications in the mathematical expressions used.

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1. Find a second solution of the differential eq. by using the formula.

xy" + y' = 0 ; y1 = ln(x)


2.

y2 = y1(x) ( ∫(e-∫P(x)dx) / (y1(x)2) )dx





3.

I found the p(x):

p(x) = 1/x


and then I plug in everything into the formula:

y2 = ln(x) ∫(e-∫((1)/(x))dx) / (ln(x)2 )dx



solve:


= ln(x) ( ∫(e^(-ln(x))) / (x)(ln(x)2))



= ∫ (1)/ (x)(ln(x))


I do not know if this is correct. I'm going to need some help.

the answer is y2 = 1


 
Last edited:
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Hang on, if P(x) = 1/x, why did you plug in ln(x) in the exponential integral term?

Edit: Also you can't multiply ln(x) into the integral.
 
Last edited:
Mugged said:
Hang on, if P(x) = 1/x, why did you plug in ln(x) in the exponential integral term?

Edit: Also you can't multiply ln(x) into the integral.

sorry. typo. the ln(x) was after integration of (1/x)
 
Rework the integral, i don't understand where you get that x in the denominator. An answer of y2 = 1 seems trivial..y2 could be any constant and it would satisfy the differential equation.
 

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