The function is .

From the graph, is increasing over .

From the graph, is decreasing over .

Now find open interval analytically.

Apply derivative to find the critical numbers.

Equate it to zero.

Therefore the critical number is .

Consider the test intervals to find the intervals of increasing and decreasing.

Consider a number in the interval .

Let .

Sign of is negative , hence is decreasing over .

Consider a number in the interval .

Let .

Sign of is positive , hence is increasing over .

is increasing over .

is decreasing over .