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Mathematics 14 Online
OpenStudy (erikaxx):

how to solve this kind of problem in linear differential equation?

OpenStudy (erikaxx):

problem is \[x \frac{ dy }{ dx } = y + x^3 +3x^2 - 2x\]

OpenStudy (loser66):

Where are you stuck?

OpenStudy (erikaxx):

\[\frac{ dy }{ dx } = \frac{ y }{ x } + x^2 + 3x - 2\]

OpenStudy (loser66):

yup

OpenStudy (erikaxx):

there, now i cant identifies the Q(x) and p(x)

OpenStudy (loser66):

\(\dfrac{dy}{dx}-\dfrac{y}{x}=x^2+3x-2\)

OpenStudy (erikaxx):

so the p(x) is x

OpenStudy (loser66):

-1/x

OpenStudy (erikaxx):

ah, and the remaing terms is the q(x)

OpenStudy (loser66):

yup

OpenStudy (erikaxx):

so IF is \[\int\limits e ^{\frac{ -1 }{ x }dx}\]

OpenStudy (erikaxx):

so e ^ -lnx

OpenStudy (loser66):

IF = 1/x

OpenStudy (loser66):

You always make mistake at this. It is NOT \[\int e^{-1/x} dx\]

OpenStudy (loser66):

\[IF = e^{\int p(x) dx}\]

OpenStudy (erikaxx):

yes so the soln is now \[(\frac{ 1 }{ x })y = [x^2 +3x - 2 ](x) (\frac{ 1 }{ x }) dx + c\]

OpenStudy (loser66):

Again, you always make mistake at (x) from the RHS, where does it come from? \[(\frac{ 1 }{ x })y = [x^2 +3x - 2 ]\color{red}{(x)(?)} (\frac{ 1 }{ x }) dx + c\]

OpenStudy (erikaxx):

what x

OpenStudy (loser66):

the red one

OpenStudy (erikaxx):

ah, i just putted it sorry its Q(X) only

OpenStudy (loser66):

And this is NOT correct also

OpenStudy (erikaxx):

why

OpenStudy (loser66):

\[\dfrac{d}{dx}(\dfrac{1}{x}*y)= Q(x)*(\dfrac{1}{x})+C\]

OpenStudy (loser66):

Then take integral both sides \[\dfrac{1}{x}y = \int Q(x) *\dfrac{1}{x} dx +C\]

OpenStudy (erikaxx):

integral of the Q(x) is \[\frac{ x^3 }{ 3 } + \frac{ 3x^2 }{ 2} - 2x(\frac{ 1 }{ x }) + c\]

OpenStudy (loser66):

NNNNNNNNNNNNO

OpenStudy (erikaxx):

huhhhhhhh

OpenStudy (loser66):

You must do multiplication before taking integral.

OpenStudy (loser66):

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