For the following system, if you isolated x in the first equation to use the Substitution Method, what expression would you substitute into the second equation?

-x + 2y = -6
3x + y = 8

A. -2y + 6
B. 2y - 6
C. 2y + 6
D. -2y - 6

Question

For the following system, if you isolated x in the first equation to use the Substitution Method, what expression would you substitute into the second equation?

-x + 2y = -6
3x + y = 8  

A. -2y + 6
B. 2y - 6
C. 2y + 6
D. -2y - 6

rogue · Answer

Well, isolating x in the first equation means that we have to get it alone on one side of the equation.
-x + 2y = -6
We can first subtract 2y from both sides.
-x + 2y - 2y = -6 - 2y
-x = -6 - 2y
Next, we just multiply both sides by negative 1 to make the x positive.
-x*-1 = (-6 - 2y)*-1
x = 6 + 2y = 2y + 6
Choice C.