Did You Solve the Differential Equation Correctly?

  • Context: MHB 
  • Thread starter Thread starter karush
  • Start date Start date
Click For Summary

Discussion Overview

The discussion revolves around the solution of the differential equation $$y^\prime +2y =xe^{-2x}, \quad y(1)=0$$. Participants explore the steps involved in finding the integrating factor and solving the equation, including the application of the product rule and integration techniques.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • Some participants confirm the integrating factor $$u(x)=e^{2x}$$ is correct, while others suggest using the notation $$\mu(x)=\exp\left(2\int \,dx\right)$$.
  • One participant expresses uncertainty about the simplification steps, particularly regarding the distribution of terms and the resulting expressions.
  • Another participant proposes checking the differentiation of $$\frac{d}{dx}\left(e^{2x}(2y)\right)$$ using the product rule to verify earlier steps.
  • A later reply presents a complete solution, deriving $$y=\frac{1}{2}(x^2-1)e^2$$, but questions whether there are any mistakes in the process.

Areas of Agreement / Disagreement

Participants generally agree on the correctness of the integrating factor but express uncertainty regarding the subsequent steps and simplifications. There is no consensus on the final solution, as some participants question the accuracy of the derived expression.

Contextual Notes

Unresolved issues include the clarity of the simplification steps and the correctness of the final expression derived for $$y$$. Participants have not fully resolved these aspects, leading to ongoing discussion.

karush
Gold Member
MHB
Messages
3,240
Reaction score
5
850
$$\displaystyle y^\prime +2y =xe^{-2x}, \quad y(1)=0$$
$$u(x)=exp\int2 \, dx = e^{2x} $$
 
Last edited:
Physics news on Phys.org
karush said:
$$\displaystyle y^\prime +2y =xe^{-2x}, \quad y(1)=0$$
$$u(x)=exp\int2 \, dx = e^{2x} $$
What is the question?
 
karush said:
is that correct

if so ill proceed

Your integrating factor is correct, but I would use the notation:

$$\mu(x)=\exp\left(2\int \,dx\right)=e^{2x}$$
 
$$\displaystyle y^\prime +2y =xe^{-2x}, \quad y(1)=0$$
$$u(x)=exp\int2 \, dx = e^{2x} $$

$$\displaystyle y^\prime +2y =xe^{-2x}, \quad y(1)=0$$
obtain u(x)
$$u(x)=exp\int2 \, dx = e^{2x} $$
distribute
$$e^{2x} y'+e^{2x} 2y=e^{2x} xe^{2x}$$
simplify
$$\frac{dy}{dx}(e^{2x} (2y))= 4xe^x $$not sure

- - - Updated - - -

MarkFL said:
Your integrating factor is correct, but I would use the notation:

$$\mu(x)=\exp\left(2\int \,dx\right)=e^{2x}$$
ok

i kinda took some more steps but ...
 
I think what you mean is:

$$\frac{d}{dx}\left(e^{2x}(2y)\right)$$

Please perform the indicated differentiation (product rule), and see if you get back to the previous step. :)
 
$$\displaystyle y^\prime +2y =xe^{-2x}, \quad y(1)=0$$
obtain u(x)
$$u(x)=exp\int2 \, dx = e^{2x} $$
distribute
$$e^{2x} y'+e^{2x} 2y=e^{2x} xe^{-2x}=x$$
simplify
$$ye^{(-2x)}=\int x dx = \frac{x^2}{2}+c$$
divide
$$y=\frac{x^2 e^{2x}}{2}+ce^{2x}$$
then
$$y(1)=\frac{e^{2}}{2}+ce^2=0 \therefore c=-\frac{1}{2}$$
finally
$$y=\frac{1}{2}(x^2-1)e^2$$

so any oops stuff
 
Last edited:

Similar threads

  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 7 ·
Replies
7
Views
1K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
Replies
7
Views
4K
  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 5 ·
Replies
5
Views
2K
Replies
9
Views
2K
  • · Replies 7 ·
Replies
7
Views
3K