SOLUTION: Solve the system by addition: x-4y=-6 2x+y=15

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Question 850997: Solve the system by addition:
x-4y=-6
2x+y=15
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
Multiply both sides of equation 2 by 4 to get

x-4y=-6
2x+y=15


x-4y=-6
4(2x+y)=4*15


x-4y=-6
8x+4y=60


Now add the equations

x-4y=-6
8x+4y=60
---------
9x+0y=54


So that means 9x=54 ----> x+=+54%2F9+=+6

Now that we know that x+=+6, we can use this to find y.

Pick any equation with x and y in it, plug in x+=+6 and solve for y. I'm going to use the first equation.

x-4y=-6

6-4y=-6

-4y=-6-6

-4y=-12

y=-12%2F%28-4%29

y=3

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So, x+=+6 and y=3