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Solving Systems of Equations by Adding
 Look
at both equations and notice whether or not the sum of one of
the variables is "0" when added. If so, add the two equations
together and solve for one of the variables. Substitute back
in one of the equations to solve for the other variable.
If the sum of one of the variables does not equal "0" , then we make the sum of one of the variables
equal "0". We can do this by multiplying one of the
equations by -1 if one of the variables has the same coefficient in both equations.
If
we do not have one set of matching coefficients in the two equations, then we make this happen by multiplying one or both of the equations by numbers that will make the sum
of one of the variables equal "O".
Solving Systems of Equations by Substitution
One
of the equations is already solved for one of the variables in terms of the other. Substitute this part of the
equation into the other equation.
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