To make a three phase generator you have to place a certain number of magnets on your stator and armature, all with proper spacing. Electromagnetism is as complex as dealing with waves and water, so you need to know how to control the field through your design.
Tutorial 20: Solving Systems of Linear Equations in Three Variables will cover systems that have three equations and three unknowns. We will look at solving them three different ways: graphing, substitution method and elimination method. This will lead us into solving word problems with systems, which will be shown in Tutorial 21: Systems of Linear Equations and Problem Solving.
The elimination method is where you actually eliminate one of the variables by adding the two equations. In this way, you eliminate one variable so you can solve for the other variable. In a two-equation system, since you have two variables, eliminating one makes the process of solving for the other quite easy.