Differential Equations and Linear Algebra (4th Edition)

Published by Pearson
ISBN 10: 0-32196-467-5
ISBN 13: 978-0-32196-467-0

Chapter 1 - First-Order Differential Equations - 1.8 Change of Variables - Problems - Page 79: 6

Answer

$f(x,y)$ is homogeneous of degree zero. $$f(x,y)=\frac{3 +10 v}{6v}$$

Work Step by Step

Given $$f(x, y)=\frac{x-2}{2 y}+\frac{5 y+3}{3 y}$$ So, we get $$f(x, y)=\frac{3x-6+10y+6}{6 y} =\frac{3x+10y}{6 y}$$ Let \begin{aligned} f (t x, ty)&=\frac{3tx+10ty}{6t y}\\ &=\frac{t(3x+10y)}{6 ty}\\ &=\frac{3x+10y}{6 y}\\ &=f(x,t) \end{aligned} Thus, $f(x,y)$ is homogeneous of degree zero. Transforming the given function \begin{aligned}f(x, y)&=\frac{3 \frac{x}{x}+10 \frac{y}{x}}{6 \frac{y}{x}}\\ &=\frac{3 +10 \frac{y}{x}}{6 \frac{y}{x}} \\ \text{Put} \ \ \ v=\frac{y}{x} \ \ \ \text{so, we get}\\ f(x,y)&=\frac{3 +10 v}{6v} \end{aligned}
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