Step 1:

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The function is $\"\"$ , point is $\"\"$ and vector is $\"\"$ .

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The directional derivative of the function $\"\"$ in the direction of a unit vector $\"\"$ is

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$\"\"$ .

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Consider $\"\"$ .

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Apply partial derivative on each side with respect to $\"\"$ .

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$\"\"$

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Substitute $\"\"$ in $\"\"$ .

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$\"\"$

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Apply partial derivative on each side with respect to $\"\"$ .

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$\"\"$

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Substitute $\"\"$ in $\"\"$ .

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$\"\"$

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Step 2:

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Here v is not a unit vector, but unit vector u is in the direction of v is $\"\"$ .

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$\"\"$

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The directional derivative of the function $\"\"$ at a point $\"\"$ in the direction of a unit vector $\"\"$ is

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$\"\"$

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$\"\"$ .

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Solution :

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$\"\"$ .