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

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Homework Help Overview

The discussion revolves around an initial value problem in differential equations, specifically focusing on the integration and manipulation of logarithmic expressions. Participants are examining their steps in solving the equation and verifying their results against given initial conditions.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants share their integration steps and how they derived expressions for y. There are questions about the correctness of constants derived from initial conditions, particularly regarding the interpretation of logarithmic results. Some participants express confusion over their calculations and seek clarification on specific steps.

Discussion Status

Multiple interpretations of the integration and initial condition application are being explored. Some participants have provided alternative approaches, but there is no explicit consensus on the correct solution. Guidance has been offered in the form of re-evaluating steps and assumptions.

Contextual Notes

Participants are working under the constraints of a homework assignment, which may impose specific requirements for the format of their answers. There is mention of potential errors in previous calculations that participants are attempting to rectify.

mr_coffee
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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:
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i get that
( \ln y )^5 = x^5 + C
and
y = e^{\frac{x}{5}} e^C
then when y(1) = e^2
we have
e^2 = e^\frac{1}{5} e^C
solving for C
C = \frac{9}{5}
then
y = e^{\frac{x}{5} + \frac{9}{5}}
 
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:
So we have after integrating, then solving for y:

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

Filling in the initial condition:

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}

So we conclude:

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

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