Calculus (3rd Edition)

Published by W. H. Freeman
ISBN 10: 1464125260
ISBN 13: 978-1-46412-526-3

Chapter 17 - Line and Surface Integrals - 17.1 Vector Fields - Exercises - Page 919: 25

Answer

\begin{align*} \mathbf{div(F)} &=1-4xz-x+2zx^2\\ \text{curl} \mathbf{(F)}&=\left( -1\right)i - \left( 2xz^2-2x^2\right)j + \left( -y\right) k \end{align*}

Work Step by Step

Given $$\mathbf{F}=\left\langle x-2 z x^{2}, z-x y, z^{2} x^{2}\right\rangle$$ Since \begin{align*} \mathbf{div(F)}&=\frac{\partial \mathbf{F}_x}{\partial x}+\frac{\partial \mathbf{F}_y }{\partial y}+\frac{\partial \mathbf{F}_z}{\partial z}\\ &=\frac{\partial ( x-2 z x^{2})}{\partial x}+\frac{\partial ( z-x y) }{\partial y}+\frac{\partial ( z^{2} x^{2})}{\partial z}\\ &= (1-4xz)+(-x)+(2zx^2)\\ &=1-4xz-x+2zx^2 \end{align*} and \begin{align*} \text{curl} \mathbf{(F)}&=\begin{array}{|||} i&j &k\\ \frac{\partial}{\partial x}& \frac{\partial}{\partial y}& \frac{\partial}{\partial z}\\ x-2 z x^{2}& z-x y& z^{2} x^{2} \end{array} \\ &= \left( \frac{\partial( z^{2} x^{2} )}{\partial y}- \frac{\partial( z-x y)}{\partial z}\right)i - \left( \frac{\partial( z^{2} x^{2} )}{\partial x}- \frac{\partial( x-2 z x^{2} )}{\partial z}\right)j + \left( \frac{\partial( z-x y )}{\partial x}- \frac{\partial( x-2 z x^{2} )}{\partial y}\right) k\\ &= \left( -1\right)i - \left( 2xz^2-2x^2\right)j + \left( -y\right) k\\ \end{align*}
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