Question

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

2x + y = 8
-x - 3y = -12

3y + 12

-3y + 12

3y - 12

-3y - 12

@jim_thompson5910

Answer 1

solve

-x - 3y = -12

for x

Answer 2

Where would I multiply that into

Answer 3

you just need to isolate x (ie get it on one side)

Answer 4

Divide -12 by 3y?

Answer 5

no

Answer 6

Or er.. by -3y?

Answer 7

you need to move over the -3y, but you don't divide

Answer 8

I don't know how I'd do that >. <

Answer 9

what undoes -3y

Answer 10

Add?

Answer 11

yep, add 3y to both sides

Answer 12

-x = -15 ?

Answer 13

I think I did that wrong.

Answer 14

no you don't add 3y to -12 to get -15y

Answer 15

you just leave it as

-x = 3y - 12

so,

x = ??

Answer 16

I still don't understand.

Answer 17

-x = 3y - 12

x = -3y + 12 ...multiply everything by -1

Answer 18

so the answer is

-3y + 12

Answer 19

Why did you multiply by -1? Just curious so I can understand what you did.

Answer 20

well we had -x = 3y - 12

but we want x = ....

Answer 21

to go from -x to x, you multiply that -x by -1 to get x

Answer 22

you have to multiply everything by -1 to balance things out

Answer 23

Ohh, okay.