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

do you know how to proceed?

Answer 2

No not really

Answer 3

But i would choose A

Answer 4

how did you reach A can you please explain?

Answer 5

-x - 2y = -4 Equation 1
3x + y = 12 Equation 2

To isolate x in Equation 1, you need to add 2y to both sides of the equal sign.
-x - 2y + 2y = -4 + 2y
-x = -4 + 2y And that is equation 3

Before we can use the equation 3 substitution, we have a slight problem to correct.
Notice that equation 3 is in terms of negative x, and equation 2 has a positive x terrm.
So to change the polarity of the x term in equation 3, multiply both sides by (-1)
(-1)(-x) = (-1)(-4 + 2y)
x = 4 - 2y

Now just substitute (4 - 2y) for x in equation 2.
What do you get @shannon342

Answer 6

-2y+4?

Answer 7

since x is negative in the first equation, should the second be also negative?

Answer 8

Yes, that is what I got

Answer 9

Thanks for the help :)

Answer 10

np can i get a medal :) ?

Answer 11

ty