Simplex Method on Linear Programming

[Guest]

Hi, I have to do some homework, and my teacher wants me to explain how the Simplex method can be used to decide if a linear programming problem is:
a) Infeasible
b) unlimited

Although I know how to solve a problem with simplex, it's hard for me to put in words this questions, so someone could help me explaining this?

[mycalsuite]

Infeasible: According to the Simplex approach, the problem is infeasible if Phase I concludes with a positive value for the artificial objective function (some artificial variables remain > 0). This indicates that no feasible solution satisfies all requirements.

Unbounded: The problem is unbounded if, during an iteration, an entering variable is discovered but no departing variable (all pivot column entries ≤ 0). This allows the objective to grow indefinitely.