Calculus 10th Edition

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

Chapter 15 - Vector Analysis - 15.1 Exercises - Page 1049: 55

Answer

$\text{Potential function: } f(x, y, z) = \frac{xz}{y} + C$

Work Step by Step

\[ \mathbf{F}(x, y, z) = \frac{z}{y}\mathbf{i} - \frac{xz}{y^2}\mathbf{j} + \frac{x}{y}\mathbf{k} \] \[ \nabla \times \mathbf{F} = \begin{vmatrix} \mathbf{i} & \mathbf{j} & \mathbf{k} \\ \dfrac{\partial}{\partial x} & \dfrac{\partial}{\partial y} & \dfrac{\partial}{\partial z} \\ \dfrac{z}{y} & -\dfrac{xz}{y^2} & \dfrac{x}{y} \end{vmatrix} \] \[ = \left(\frac{\partial R}{\partial y} - \frac{\partial Q}{\partial z}\right)\mathbf{i} - \left(\frac{\partial R}{\partial x} - \frac{\partial P}{\partial z}\right)\mathbf{j} + \left(\frac{\partial Q}{\partial x} - \frac{\partial P}{\partial y}\right)\mathbf{k} \] \[ = \left(-\frac{x}{y^2} - \left(-\frac{x}{y^2}\right)\right)\mathbf{i} - \left(\frac{1}{y} - \frac{1}{y}\right)\mathbf{j} + \left(-\frac{z}{y^2} - \left(-\frac{z}{y^2}\right)\right)\mathbf{k} \] \[ = 0 \] \[ \therefore \mathbf{F} \text{ is conservative.} \] \[ f(x, y, z) = \int f_x\,dx = \int \frac{z}{y}\,dx = \frac{xz}{y} + g(y, z)+K1 \] \[ f(x, y, z) = \int f_y\,dy = \int -\frac{xz}{y^2}\,dy = \frac{xz}{y} + h(x, z)+K2 \] \[ f(x, y, z) = \int f_z\,dz = \int \frac{x}{y}\,dz = \frac{xz}{y} + k(x, y) +K3 \] \[ \boxed{f(x, y, z) = \frac{xz}{y} + K} \]
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