Edward C. answered • 03/07/16
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Caltech Grad for math tutoring: Algebra through Calculus
Substitution means that you want to solve one of the equations for one of the variables, and then substitute that expression for the variable in the other equation.
You can solve either equation for either variable. In this case if you solve the first equation for y you won't have to do any division, and you'll end up with y = some function of x.
Then substitute that expression for y into the second equation (this means that wherever you see a y in the second equation you replace it with what y is equal to in terms of x). This will give you a single equation in one unknown (x) which you can solve by normal algebraic methods. Once you know what x is equal to just plug that value back into either of the original equations and solve for y. Once you have both values check that they satisfy both equations.
