Suppose that $\operatorname { grad } f ( 1 , - 1 ) = \vec { v }$ , with $\| \vec { v } \| = 4$ (a)What is the directional derivative of f at (1, -1)in the direction of $3 \vec { v }$ ?
(b)What is the smallest value of the directional derivative of f at (1, -1)among all possible directions?

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The Answer of Suppose that $\operatorname { grad } f ( 1 , - 1 ) = \vec { v }$ , with $\| \vec { v } \| = 4$ (a)What is the directional derivative of f at (1, -1)in the direction of $3 \vec { v }$ ?
(b)What is the smallest value of the directional derivative of f at (1, -1)among all possible directions?

Suppose That grad⁡f(1,−1)=v⃗\operatorname { grad } f ( 1 , - 1 ) = \vec { v }gradf(1,−1)=v

Suppose That $\operatorname { grad } f ( 1 , - 1 ) = \vec { v }$