Elementary Differential Equations and Boundary Value Problems 9th Edition

Published by Wiley
ISBN 10: 0-47038-334-8
ISBN 13: 978-0-47038-334-6

Chapter 4 - Higher Order Linear Equations - 4.1 General Theory of nth Order Linear Equations - Problems - Page 224: 16

Answer

$W(x,x^2,\frac{1}{x})(t)=\frac{6}{x}$

Work Step by Step

we verify the given functions are the solutions of the differential equation by plugging them into it: $y=x\;\;\;\rightarrow \;\;\;x^3({x})'''+x^2({x})''-2x(x)'+2(x)=\;0+0-2x+2x=0\\\\$ $y=x^2\;\;\;\rightarrow \;\;\;x^3({x^2})'''+x^2({x^2})''-2x(x^2)'+2(x^2)=\;0+2x^2-4x^2+2x^2=0\\\\$ $y=\frac{1}{x}\;\;\;\rightarrow \;\;\;x^3({\frac{1}{x}})'''+x^2({\frac{1}{x}})''-2x(\frac{1}{x})'+2(\frac{1}{x})=\;\frac{-6}{x}+\frac{2}{x}+\frac{2}{x}+\frac{2}{x}=0\\\\$ $W(x,x^2,\frac{1}{x})(t)=\begin{vmatrix} x & x^2 & \frac{1}{x}\\ (x)' & ({x^{2}})' & (\frac{1}{x})'\\ (x)''&({e^{2}})'' & (\frac{1}{x})'' \end{vmatrix}\;\;=\;\;\begin{vmatrix} x & x^2 & \frac{1}{x}\\ 1 & 2x & \frac{-1}{x^2}\\ 0 & 2 & \frac{2}{x^3} \end{vmatrix}\;\;=$ $x.\begin{vmatrix} 2x & \frac{-1}{x^2}\\ 2 & \frac{2}{x^3} \end{vmatrix}\;\;-\;\begin{vmatrix} x^2 & \frac{1}{x}\\ 2 & \frac{2}{x^3} \end{vmatrix}\;=\;$ $x.(\frac{4}{x^2}+\frac{2}{x^2})\;\;-\;(\frac{2}{x}-\frac{2}{x})\;=\; \frac{6}{x}-0\;=\;\frac{6}{x}$ $W(x,x^2,\frac{1}{x})(t)=\frac{6}{x}$
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