By first principles, the derivative is

Use the binomial theorem to expand the numerator:


where

The first term is eliminated, and the limit is

A power of
in every term of the numerator cancels with
in the denominator:

Finally, each term containing
approaches 0 as
, and the derivative is

Ofcourse it is a linear function
why because every of x value of this function is 23 in result always
... so when we draw a chart it will be line on 23 coordinate ;)