A function defined by , where , is called the logarithm of to the base . The common logarithmic function is written as .

We shall prove formula for derivative of natural logarithm function using by definition or first principle method.

Let us suppose that the function of the form

First we take the increment or small change in the function.

Putting the value of function in the above equation, we get

Dividing both sides by , we get

Multiplying and dividing the right hand side by , we have

Taking limit of both sides as , we have

Consider , as then , we get

Using the relation from limit , we have

__Example__**:** Find the derivative of

We have the given function as

Differentiation with respect to variable , we get

Using the rule, , we get