Now in order to solve this system by using substitution, we need to solve (or isolate) one variable. I'm going to solve for y.
Start with the second equation (Either equation will work, but y is easier to isolate in this equation)
Subtract from both sides
Rearrange the equation
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Since , we can now replace each in the first equation with to solve for
Plug in into the first equation. In other words, replace each with . Notice we've eliminated the variables. So we now have a simple equation with one unknown.