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Increasing if f' >0 and decreasing if f'<0

Step-by-step explanation:

Difference quotient got by getting

will be greater than 0 if function is increasing otherwise negative

Here h is a small positive value.

In other words, we find that whenever first derivative of a function f(x) is positive the function is increasing.

Here given that for x1, x2 where x1<x2, we have

if f(x1) <f(x2) then the function is decreasing.

Or if x1<x2 and if f(x1) >f(x2) for all x1, and x2 in I the open interval we say f(x) is decreasing in I.