Andes recognizes "g" as a predefined constant denoting the magnitude of the acceleration due to gravity in the region of the problem. However it does not know the value of g for the problem. If a problem is set near the surface of the moon, the value of g will be different than it is near the surface of the Earth.

Therefore, although you do not have to define g, you still have to enter an equation giving the value of g in your solution.

Andes treats 9.8 m/s^2 as the value of g near the surface of the Earth. For other regions you will be given the appropriate value of g.

Note that g denotes a vector magnitude so has a positive value.