Question: Value of x in a System

Comment on Value of x in a System

How come you can't take one equation, solve for y in terms of x, and then substitute that y-value back into the equation and subsequently solve for x?
gmat-admin's picture

Try it, and you'll find a problem.

The reason you'll find a problem is that both equations are equivalent. That is, both equations can be written as 6x - 3y = -9 (or we could write both equations as 2x - y = -3).

So, we don't have two unique equations with 2 variable. Instead, we have ONE equation with 2 variables.

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