$\"\"$

Directional derivative of a function :

If the unit vector is $\"\"$ , then the directional derivative of the function $\"\"$ is $\"\"$ .

$\"\"$

Find directional derivative of the function.

The function is $\"\"$ and the unit vector is $\"\"$ .

Differentiate $\"\"$ partially with respect to $\"\"$ .

$\"\"$

Differentiate $\"\"$ partially with respect to $\"\"$ .

$\"\"$

Directional derivative, $\"\"$ .

Substitute the values $\"\"$ in above equation.

$\"\"$

$\"\"$ .

$\"$

The directional derivative is $\"\"$ .