$\"\"$

\

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 $\"\"$ , the point is $\"\"$ and the vector is $\"\"$ .

\

Find the unit vector $\"\"$ :

\

$\"\"$

\

$\"\"$ .

\

$\"\"$

\

Compare $\"\"$ with $\"\"$ .

\

$\"\"$ and $\"\"$ .

\

Directional derivative, $\"\"$ .

\

Substitute the values $\"\"$ , $\"\"$ , and the point $\"\"$ in above equation.

\

$\"\"$

\

$\"\"$ .

\

$\"$

\

The directional derivative is $\"\"$ .