Calculus 10th Edition

Published by Brooks Cole
ISBN 10: 1-28505-709-0
ISBN 13: 978-1-28505-709-5

Chapter 8 - Integration Techniques, L'Hopital's Rule, and Improper Integrals - 8.2 Exercises - Page 521: 37

Answer

Picture Attached

Work Step by Step

The question asks for a plot of the slope field with a computer algebra system, which is pictured above. It also asks to plot the solution to the following differential equation that satisfies $y(0) = 2$: $\frac{dy}{dx} = \frac{x}{y}*e^{\frac{x}{8}}$ This differential equation can be solved using separation of variables in the following way: $\frac{dy}{dx} = \frac{x}{y}*e^{\frac{x}{8}} \implies dy = \frac{x}{y}*e^{\frac{x}{8}} dx \implies y$ $dy = x e^{\frac{x}{8}} $ $dx $ Now, we integrate both sides: $\int y$ $dy = \int x e^{\frac{x}{8}} $ $dx $ The left side can be integrated using the power rule, for the right side we will use integration by parts. $\implies \frac{y^{2}}{2} = \int x e^{\frac{x}{8}} $ $dx $ Letting $u = x , v' = e^{\frac{x}{8}}$, we integrate by parts: $\implies \int x e^{\frac{x}{8}} $ $dx =8xe^{\frac{x}{8}} - \int 8e^{\frac{x}{8}}$ $dx $ $= 8xe^{\frac{x}{8}} - 64e^{\frac{x}{8}} + C = 8e^{\frac{x}{8}}(x-8) + C$ $\implies \frac{y^{2}}{2} = 8e^{\frac{x}{8}}(x-8) + C \implies y = \sqrt{16e^{\frac{x}{8}}(x-8) + 2C}$ Now, we impose the boundary condition of $y(0) = 2 \implies 2 = \sqrt{16e^{\frac{0}{8}}(0-8) + 2C} = \sqrt{-124 + 2C} $ $\implies 4 = -124 + 2C \implies C =66$ Thus, the plotted solution is: $y = \sqrt{16e^{\frac{x}{8}}(x-8) + 132}$
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