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 one year ago
consider the differential equation: x^3(x^21)^2(x^2+1)y''+(x+1)xy'+y=0. determine whether x=0 is a regular singular point. determine whether x=1 is a regular singular point. are there any regular singular points that are complex numbers? justify conclusions
 one year ago
consider the differential equation: x^3(x^21)^2(x^2+1)y''+(x+1)xy'+y=0. determine whether x=0 is a regular singular point. determine whether x=1 is a regular singular point. are there any regular singular points that are complex numbers? justify conclusions

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goalie2012
 one year ago
Best ResponseYou've already chosen the best response.0\[x ^{3}(x^21)^2(x^2+1)y''+(x1)xy'+y=0\]

goalie2012
 one year ago
Best ResponseYou've already chosen the best response.0the answers I got for this one were 0, 1, and i, but I'm not sure how to justify them. Are those even right to begin with?

goalie2012
 one year ago
Best ResponseYou've already chosen the best response.0if you know this one, please answer, but I'm going to write the other one since I'm having more trouble with it.

oldrin.bataku
 one year ago
Best ResponseYou've already chosen the best response.1First, rewrite it in standard form:$$y''+\frac{x(x1)}{x^3(x^21)^2(x^2+1)}y+\frac1{x^3(x^21)^2(x^2+1)}y=0$$

oldrin.bataku
 one year ago
Best ResponseYou've already chosen the best response.1To see if \(x=0\) is ordinary, we see if the coefficients of \(y'\) and \(y\) are analytic at \(x=0\); as you can see, \(y',y\) are not analytic therefore \(x=0\) is singular.

oldrin.bataku
 one year ago
Best ResponseYou've already chosen the best response.1To determine whether it is regular, we consider whether \(xp(x),x^2q(x)\) are analytic at \(x=0\) where \(p(x),q(x)\) are the coefficients of \(y',y\) respectively. Observe that neither \(xp(x),x^2q(x)\) are analytic at \(x=0\) (there is at least one factor of \(x\) remaining in the denominator) thus this is an irregular singular point.

oldrin.bataku
 one year ago
Best ResponseYou've already chosen the best response.1for the above I meant the coefficients of \(y',y\) were not singular:$$y''+\underbrace{\frac{x(x1)}{x^3(x^21)^2(x^2+1)}}_{p(x)}y+\underbrace{\frac1{x^3(x^21)^2(x^2+1)}}_{q(x)}y=0$$Note that we can simplify \(p(x)\):$$p(x)=\frac{x1}{x^2(x^21)^2(x^2+1)}$$which unfortunately is still not analytic at \(x=0\). Thus it is a singular point. Observe that \(xp(x)\) is also not analytic:$$xp(x)=\frac{x1}{x(x^21)^2(x^2+1)}$$thus \(x=0\) is an irregular singular point.

oldrin.bataku
 one year ago
Best ResponseYou've already chosen the best response.1For \(x=1\), consider simplifying \(p(x)\) a little more:$$p(x)=\frac{x1}{x^2(x^21)(x^21)(x^2+1)}=\frac1{x^2(x+1)(x^21)(x^2+1)}$$yet unfortunately it is still not analytic at \(x=1\)

oldrin.bataku
 one year ago
Best ResponseYou've already chosen the best response.1Similarly consider \((x1)p(x)\):$$(x1)p(x)=\frac{x1}{x^2(x+1)(x^21)(x^2+1)}=\frac1{x^2(x+1)^2(x^2+1)}$$which is analytic at \(x=1\)! Now, check \((x1)^2q(x)\):$$(x1)^2q(x)=\frac{(x1)^2}{x^3(x^21)^2(x^2+1)}=\frac1{x^3(x+1)^2(x^2+1)^2}$$which is also analytic at \(x=1\) hence \(x=1\) is a regular singular point

oldrin.bataku
 one year ago
Best ResponseYou've already chosen the best response.1To determine whether there are complex singular points, observe the roots of our denominator of \(p(x)\):$$x^2(x+1)(x^21)(x^2+1)=0$$we observe we have singularities at \(x^2+1=0\) i.e. \(x=\pm i\). To determine whether they're regular, consider whether \((xi)p(x),(x+i)p(x)\) still have the singular point:$$(xi)p(x)=\frac{xi}{x^2(x+1)^2(x^2+1)}=\frac1{x^2(x+1)^2(x+i)}\\(x+i)p(x)=\frac{x+i}{x^2(x+1)^2(x^2+1)}=\frac1{x^2(x+1)^2(xi)}$$nope! Since \(q(x)\)'s denominator has the same root with the same multiplicity you can conclude \((x\pm i)q(x)\) will also be analytic at \(x=\pm i\). Hence \(x=\pm i\) are regular singular points.
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