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This site helps you understand S.O.L.E. or system of linear equations. A "system" of equations is a set or collection of equations that you deal with all together at once. Their are two directions you can take when you solve S.O.L.E. you can use the substitution method where you take one equations and plug it in for the other equation. The elimination method is when you remove a variable at the start. Both of these method could be used in a linear equation.
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