Chapter 14 - Section 14.6 - Directional Derivatives and the Gradient Vector - 14.6 Exercise - Page 957: 10

a)$\nabla f=$ b)$\nabla f_{(0, 1, -1)}=<-1,2,0>$ c)$D_uf_{(0, 1, -1)}=-\frac{8}{13}$

$\nabla f=$ $\nabla f_{(0, 1, -1)}=<-1,2,0>$ $D_uf_{(0, 1, -1)}=\nabla f_{(0, 1, -1})\cdot u=<0, 1, -1>\cdot<\frac{3}{13}, \frac{4}{13},\frac{12}{13}>=-\frac{8}{13}$