Using GC to determine the nature of stationary points

Suppose we are required to determine the nature of stationary points for the following:

Using TI-84 Plus (OS 2.55) 

Observation of stationary points:

Left stationary point: First derivative changes from +ve to -ve. Therefore, it is a maximum point

Middle stationary point: No change in sign of deriative. Therefore, it is a point of inflexion.

Right stationary point. First derivative changes from -ve to +ve. Therefore, it is a minimum point