are split points that split up the domain into three intervals

and

To determine the sign of in each of these intervals use a value of x in the interior of the interval

To determine the sign of in the interval, , for example, you could use

If , then f(x) is increasing in the interval

If , then f(x) is decreasing in the interval

Determine the sign of in the other two intervals

are split points for the second derivative

They split up the domain into the intervals

and

Determine the sign of in each interval

If , then f(x) is concave up

If , then f(x) is concave down