Intial Value problem, Diff EQ, my steps look right but answer = wrong wee

In summary, the person was trying to solve for y using ln(e^2), but instead got the wrong answer due to a mistake with the exponent.
  • #1
mr_coffee
1,629
1
Hello everyone I'm stuck on this problem:
http://cwcsrv11.cwc.psu.edu/webwork2_files/tmp/equations/18/0c06a4e72ea888ea65443a46afd42f1.png
http://cwcsrv11.cwc.psu.edu/webwork2_files/tmp/equations/90/dff750d2ab4fefb41eccca8ce709a01.png
Looks simple enough but the answer they said is wrong. Here is my work:
(ln(y))^4/y dy = x^4 dx;
after integrating both sides:
1/5 * ln(y)^5 = (x^5/5) + C;

I raised both sides to e^
y^5 = [e^(x^5)*e^(5C)]
y = [e^(x^5)*e^(5C)]^(1/5);

now i subed in the I.C.
e^2 = (e^(5C))^(1/5);
e^2 = e^C;
ln(e^2) = C;
2 = C;

y = (e^(x^5)*e^10)^(1/5) which was wrong!~ wee! :cry:

Any help would be great! Linux isn't liking my scanner at the moment so I'm going to have to type out my problems for now :(
I think i screwd pu here but not sure:
ln(e^2) = C;
is that
2 = C or
ln(2*e) = C
 
Last edited by a moderator:
Physics news on Phys.org
  • #2
i get that
[tex] ( \ln y )^5 = x^5 + C [/tex]
and
[tex] y = e^{\frac{x}{5}} e^C [/tex]
then when [tex] y(1) = e^2 [/tex]
we have
[tex] e^2 = e^\frac{1}{5} e^C [/tex]
solving for C
[tex] C = \frac{9}{5} [/tex]
then
[tex] y = e^{\frac{x}{5} + \frac{9}{5}} [/tex]
 
  • #3
Thanks for the responce but
i submitted it and is also wrong!
http://cwcsrv11.cwc.psu.edu/webwork2_files/tmp/equations/15/e1bf20f7f42406e76279e9bc8fe45a1.png
 
Last edited by a moderator:
  • #4
So we have after integrating, then solving for y:

[tex]\frac{{\left( {\ln y} \right)^5 }}{5} = \frac{{x^5 }}{5} + c \Leftrightarrow y = e^{\left( {x^5 + 5c} \right)^{1/5} } [/tex]

Filling in the initial condition:

[tex]e^2 = e^{\left( {1 + 5c} \right)^{1/5} } \Leftrightarrow 2 = \left( {1 + 5c} \right)^{1/5} \Leftrightarrow 32 = 1 + 5c \Leftrightarrow c = \frac{{31}}{5}[/tex]

So we conclude:

[tex]y = e^{\left( {x^5 + 31} \right)^{1/5} } [/tex]
 
  • #5
TD you are the man, I'm e-mailing u some money hah. Thanks !
 
  • #6
yes i redid the problem and got the same answer... i made a mistake with the exponent :( sorry about that
 

1. What is an initial value problem?

An initial value problem is a type of differential equation that involves finding a function that satisfies the equation and a given set of initial conditions. These conditions typically involve specifying the value of the function at a certain point or the value of its derivative at a certain point.

2. How do I solve an initial value problem?

To solve an initial value problem, you will need to use a method that is appropriate for the type of differential equation. This could include separation of variables, substitution, or using an integrating factor. Once you have solved the equation, you can use the given initial conditions to determine the constants and find the specific solution.

3. What are some common mistakes when solving initial value problems?

Some common mistakes when solving initial value problems include incorrectly applying the chosen method, making errors in algebraic manipulations, and not checking the solution for accuracy. It is important to carefully follow the steps and double check your work to avoid these mistakes.

4. What should I do if my steps look right but the answer is wrong?

If your steps look correct but you are getting the wrong answer, it is possible that you made a small error in one of your calculations. Try going back through your work and checking each step carefully. You can also try using a different method to solve the problem to see if you get the same result.

5. How can I check if my solution to an initial value problem is correct?

To check if your solution to an initial value problem is correct, you can substitute the function and its derivative into the original equation and see if it satisfies the equation. You can also plug in the given initial conditions to see if they are satisfied. Additionally, you can use an online calculator or software program to verify your solution.

Similar threads

  • Calculus and Beyond Homework Help
Replies
1
Views
968
  • Calculus and Beyond Homework Help
Replies
18
Views
2K
  • Calculus and Beyond Homework Help
Replies
4
Views
2K
  • Calculus and Beyond Homework Help
Replies
5
Views
1K
  • Calculus and Beyond Homework Help
Replies
12
Views
1K
  • Calculus and Beyond Homework Help
Replies
3
Views
1K
  • Calculus and Beyond Homework Help
Replies
3
Views
1K
  • Calculus and Beyond Homework Help
Replies
4
Views
1K
  • Calculus and Beyond Homework Help
Replies
1
Views
8K
  • Calculus and Beyond Homework Help
Replies
4
Views
2K
Back
Top