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 = -4 3x + y = 12
a. -2y - 4
b. 2y - 4
c. 2y + 4
d. -2y + 4

Answer 1

$-x-2y=-4 \\ 3x+y=12 \\ \\ \hbox{the first equation:} \\ -x-2y=-4 \ \ \ \ \ \ |+2y \\ -x=2y-4 \ \ \ \ \ \ \ \ |\times (-1) \\ x=-2y+4$

The expression you would substitute for x is -2y+4. The answer is d.