Answer:
a)
.
b) 
Step-by-step explanation:
Given a function
, this function has the following gradient:
.
(a) find the gradient of f
We have that
. So


.
.

(b) find the directional derivative of f at (2, 4, 0) in the direction of v = i + 3j − k.
The directional derivate is the scalar product between the gradient at (2,4,0) and the unit vector of v.
We have that:

.

The vector is 
To use v as an unitary vector, we divide each component of v by the norm of v.

So

Now, we can calculate the scalar product that is the directional derivative.

???????what that guy said
The answer is D. I am sure of this. Brainpower? Have a great day!
Hi there! With equations like this we want to get our variable on one side and and our constant on the other.
So with 2x + 3 = -7 you'd subtract the constant 3 from both sides of the equal sign to get 2x = -10, then you'd divide both sides by 2 to get x = -5. If you double check your work by replacing x in the original equation with our answer we'd find that 2(-5) + 3 = -7 is correct.
Hope you find this helpful :)
Slope = rise/run = 10/50 = 1/5