SOLUTION: 7x-6y=-12 6x+7y=99 The directions are solve by the elimination method. I have tried by multiplying the top equation by 7 and the bottom by 6 since there was already a negative o

Algebra ->  Coordinate Systems and Linear Equations  -> Lessons -> SOLUTION: 7x-6y=-12 6x+7y=99 The directions are solve by the elimination method. I have tried by multiplying the top equation by 7 and the bottom by 6 since there was already a negative o      Log On


   

Question 917949: 7x-6y=-12
6x+7y=99
The directions are solve by the elimination method.
I have tried by multiplying the top equation by 7 and the bottom by 6 since there was already a negative on top. I then got 49x-42y=-84 and 36x+42y=594 . I then added them together and got 85x=510 which equals x=6. Then I plugged 6 in for x In the equation 7x-6y=-12 and got y=-9.
But when I put in the answer in mathxl, it said it was wrong. Please help me figure out what I did wrong and understand how to work this problem.
Answer by KMST(5328) About Me  (Show Source):
You can put this solution on YOUR website!
When you plugged 6 in for x In the equation 7x-6y=-12 , you should get
7%2A6-6y=-12--->42-6y=-12--->42%2B12-6y=0--->54-6y=0--->54=6y--->54%2F6=y--->highlight%28y=9%29 .
That checks out, because when you plug x=6 and y=9 back into the original equations, you get
7%2A6-6%2A9=42-54=-12 and 6%2A6%2B7%2A9=36%2B63=99 .
You got y=-9 because plus and minus signs sometimes turn into each other just to trip students.
It happens to all of us (or at least to most of us).
It did cost me an exam, mostly because instead of moving on to the next problem, I kept working on and reviewing the same problem where I had realized something was off.