$\"\"$

Let $\"\"$ be a differential function of period $\"\"$ .

Consider the periodic function is $\"\"$ .

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

$\"\"$

$\"\"$ .

A function returning to the same value at regular intervals.

The rate of change of $\"\"$ is equal to the rate of change in $\"\"$ .

$\"\"$ is periodic.

$\"\"$

The function is $\"\"$ .

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

$\"\"$

$\"\"$ .