Multivariable Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 0-53849-787-4
ISBN 13: 978-0-53849-787-9

Chapter 17 - Second-Order Differential Equations - 17.1 Exercises - Page 1172: 15

Answer

$y=c_{1}e^{\frac{-3x}{5}}+c_{2}e^{x}$ As $x$ approches $\pm \infty$, $y$ approaches either $0$ or $\pm \infty$.

Work Step by Step

$5\frac{d^{2}y}{dx^{2}}-2\frac{dy}{dx}-3y=0$ $5y''-2y'-3y=0$ Use auxiliary equation $5r^{2}-2r-3=0$ $5r^{2}-2r-3=0$ $5r^{2}+(-5r+3r)-3=0$ $(5r^{2}-5r)+(3r-3)=0$ $5r(r-1)+3(r-1)=0$ $(5r+3)(r-1)=0$ $r_{1}=1, r_{2}=-\frac{3}{5}$ Formula 8 $y=c_{1}e^{r_{1}x}+c_{2}e^{r_{2}x}$ $y=c_{1}e^{\frac{-3x}{5}}+c_{2}e^{x}$ Therefore, $f(x)=e^{\frac{-3x}{5}}$ and $g(x)=e^{x}$ are the basic solutions. FIRST GRAPH $y=f(x)$ is the blue curve. $y=g(x)$ is the red curve. SECOND GRAPH $y=f(x)$ is the blue dotted curve. $y=g(x)$ is the red dotted curve. $y=f+g$ is the solid black curve. THIRD GRAPH $y=f(x)$ is the blue dotted curve. $y=g(x)$ is the red dotted curve. $y=f-g$ is the solid black curve. FOURTH GRAPH $y=f(x)$ is the blue dotted curve. $y=g(x)$ is the red dotted curve. $y=-f+g$ is the solid black curve. As $x$ approches $\pm \infty$, $y$ approaches either $0$ or $\pm \infty$.
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