Wronskian and Second Order Differential Equations

metgt4
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Homework Statement



Given a second order differential equation:

y'' + P(x)y' + Q(x)y = 0

If y1(x) and y2(x) are linearly independent solutions of the DE, what form does Abel's Equation give for W(y1(x), y2(x))? If we assume that one solution y1(x) is known, what first order DE results from a reduction of order using y1(x)?

The Attempt at a Solution



I know that Abel's Equation gives the form of

W(y1(x), y2(x)) = Ce^{\int}P(x)dx

Where C is a constant

But how would you use an unknown y1(x) to do a reduction of order on the equation?
 
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This PDF explains it. http://www.ux1.eiu.edu/~wrgreen2/research/Abel.pdf
See the bottom of page 1.
 
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There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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