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Q. 36

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Calculus
Found in: Page 989
Calculus

Calculus

Book edition 1st
Author(s) Peter Kohn, Laura Taalman
Pages 1155 pages
ISBN 9781429241861

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Short Answer

Gradients: Find the gradient of the given function, and find the direction in which the function increases most rapidly at the specified point P.

f(x, y ,z) = ln(x + y + z), P = (e, 0, −1) .

The gradient is f(x,y,z)=1x+y+z,1x+y+z,1x+y+z and the direction in which increases most rapidly at p=(e,0,-1) isf(e,0,-1)=1e-1,1e-1,1e-1

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Step by Step Solution

Step 1. Given 

f(x, y ,z) = ln(x + y + z)

Step 2.  Finding gradient of f(x, y ,z) = ln(x + y + z)

The gradient of a function f(x,y,z) is defined by f(x,y,z)=fxi+fyj+fzk.here , f(x, y,z) = ln(x + y + z).So , its gradient is given by,f(x,y,z)=(ln(x + y + z))xi+(ln(x + y + z))yj+(ln(x + y + z))zk =1x+y+zi+1x+y+zj+1x+y+zk.Hence ,the gradient is f(x,y,z)=1x+y+z,1x+y+z,1x+y+z.

Step 3. Finding points in the direction in which f increases .

As the gradient of a function at a point p, points in the direction in which f increases most rapidly Here p=(e,0,-1), so f(e,0,-1)=1e-1i+1e-1j+1e-1k Hence the direction in which increases most rapidly at p=(e,0,-1) is f(e,0,-1)=1e-1,1e-1,1e-1

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