maximum rate of change: f(x,y,z) = sqrt(xyz), p = (3,3,2)

moy1989

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Oct 11, 2007
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Determine the maximum rate of change of the function f at the point p, and in the direction in which it occurs (written as a unit vector).

f(x,y,z) = sqrt(xyz), p = (3,3,2)

I only need help on the first part of this problem:

This is what I did:

Gradient of f = (1/2)(x * y^2 * z^2, x^2 * y * z^2, x^2 * y^2 * z)

I evaluated the Gradient of f at (3,3,2) and attained (54, 54, 81)

So, the maximum rate of change is the magnitude of the Gradient and that is sqrt(54^2 + 54^2 + 81^2) = 111.32385.

Can anyone spot my mistake here? I got the second part right which is just the Gradient vector divided by the magnitude 111.32385; I don't understand how the above is wrong.

Thanks for any help.
 
Re: maximum rate of change

moy1989 said:
Determine the maximum rate of change of the function f at the point p, and in the direction in which it occurs (written as a unit vector).

f(x,y,z) = sqrt(xyz), p = (3,3,2)

I only need help on the first part of this problem:

This is what I did:

Gradient of f = (1/2)(x * y^2 * z^2, x^2 * y * z^2, x^2 * y^2 * z) <<< Please show work

I evaluated the Gradient of f at (3,3,2) and attained (54, 54, 81)

So, the maximum rate of change is the magnitude of the Gradient and that is sqrt(54^2 + 54^2 + 81^2) = 111.32385.

Can anyone spot my mistake here? I got the second part right which is just the Gradient vector divided by the magnitude 111.32385; I don't understand how the above is wrong.

Thanks for any help.
 
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