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Mathematics 19 Online
OpenStudy (asylum15):

- Separable Equation

OpenStudy (asylum15):

\[\frac{ dy }{ dx } = \frac{ 2y }{ x(y-5) }\] Solve for general/particular solution.

OpenStudy (anonymous):

\[ \int \frac{y-5}{y}\frac{dy}{dx}dx=\int\frac{2}{x}dx \]

OpenStudy (anonymous):

Remember \((dy/dx)dx = dy\)

OpenStudy (anonymous):

All I did was: 1) Multiply both sides by \(y-5\) 2) Divide both sides by \(y\) 3) Integrate both sides with respect to \(x\) No magic, no abuse of notation.

OpenStudy (asylum15):

hey

OpenStudy (asylum15):

The hardest ones I find easiest, and these ones I'm thinking too much on, may I ask you one other thing?

OpenStudy (anonymous):

Go ahead.

OpenStudy (asylum15):

\[(1+x^3).\frac{ dy }{ dx } = x^2y\]

OpenStudy (asylum15):

How would you isolate dy and dx?

OpenStudy (anonymous):

\[ \int \frac{1}{y}\frac{dy}{dx}dx=\int \frac{x^2}{1+x^3}dx \]

OpenStudy (anonymous):

Whenever you want to multiply by \(dx\), DON'T! Instead integrate by \(x\) and it will go away nicely.

OpenStudy (asylum15):

I can integrate etc, use indice rules, ln all the ''difficult'' operations. I just always find it tough to transpose in the beginning for some reason..

OpenStudy (anonymous):

What you'll have is: \[ f(x)g(y)\frac{dy}{dx}=h(x)k(y) \]And what you end up with is: \[ \int \frac{g(y)}{k(y)}\frac{dy}{dx}dx=\int \frac{h(x)}{f(x)}dx \]

OpenStudy (anonymous):

\(\color{blue}{\text{Originally Posted by}}\) @Asylum15 \[\frac{ dy }{ dx } = \frac{ 2y }{ x(y-5) }\] Solve for general/particular solution. \(\color{blue}{\text{End of Quote}}\) \[(1)(1) \frac{dy}{dx}=\left(\frac{2}{x}\right)\left(\frac{y}{y-5}\right) \\ .\\ f(x)=1\\ g(y)=1\\ h(x)=\frac{2}{x}\\ k(y)=\frac{y}{y-5} \]

OpenStudy (asylum15):

So the integral of \[\frac{ x^2 }{ (1+x^3) }\] = \[\frac{ x^2 }{ 1 } + \frac{ x^2 }{ x^3}\]?

OpenStudy (anonymous):

No, that isn't how fractions work.

OpenStudy (asylum15):

My apologies :|

OpenStudy (asylum15):

\[ \frac{ \ln(x^3+1) }{ 3 }\]

OpenStudy (anonymous):

Yeah, whoops let me rewrite that.

OpenStudy (asylum15):

Thanks for your help btw :)

OpenStudy (anonymous):

\[ \int \frac{x^2}{1+x^3}dx = \int \frac{1}{1+x^3} \frac{d(1+x^3)}{3} = \int \frac{1}{3u}du \]

OpenStudy (asylum15):

ah!

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