Calculus 10th Edition

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

Chapter 13 - Functions of Several Variables - 13.5 Exercises - Page 913: 33

Answer

\begin{aligned} \frac{\partial w }{\partial x} =\frac{y+w}{z-x} \\ \end{aligned} \begin{aligned} \frac{\partial w }{\partial y} =\frac{x+z}{z-x} \\ \end{aligned} \begin{aligned} \frac{\partial w }{\partial z} =\frac{y-w}{z-x} \\ \end{aligned}

Work Step by Step

Given $$x y+y z-w z+w x=5$$ $$\Rightarrow x y+y z-w z+w x-5=0$$ by letting $$F(x,y,z,w)= x y+y z-w z+w x-5$$ So, we have $$F_x(x,y,z,w)=\frac{\partial F(x,y,z,w)}{\partial x}= y+w\\ $$ $$F_y(x,y,z,w)=\frac{\partial F(x,y,z,w)}{\partial y}= x+z$$ $$F_z(x,y,z,w)=\frac{\partial F(x,y,z,w)}{\partial z}=y-w$$ $$F_w(x,y,z,w)=\frac{\partial F(x,y,z,w)}{\partial w}=-z+x$$ Also, we get \begin{aligned} \frac{\partial w }{\partial x}&=-\frac{F_{x}(x, y,z,w)}{F_{w}(x, y,z,w)} \\ &=-\frac{y+w}{-z+x} \\ &=\frac{y+w}{z-x} \\ \end{aligned} \begin{aligned} \frac{\partial w }{\partial y}&=-\frac{F_{y}(x, y,z,w)}{F_{w}(x, y,z,w)} \\ &=-\frac{x+z}{-z+x} \\ &=\frac{x+z}{z-x} \\ \end{aligned}\begin{aligned} \frac{\partial w }{\partial z}&=-\frac{F_{z}(x, y,z,w)}{F_{w}(x, y,z,w)} \\ &=-\frac{y-w}{-z+x} \\ &=\frac{y-w}{z-x} \\ \end{aligned}
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