$\"\"$

Differentiation rule :

Suppose $\"\"$ and $\"\"$ are differentiable vector functions, $\"\"$ is a scalar and $\"\"$ is a real valued function.

Then $\"\"$ .

$\"\"$

Consider the two vectors $\"\"$ and $\"\"$ .

$\"\"$

$\"\"$ .

Therefore, $\"\"$ .

$\"\"$

$\"\"$ .