How do you solve the following system?: -8x+3y=12 , 8x-9y= 12 8x+3y=12,8x9y=12

1 Answer
Mar 14, 2018

x=-3, y=-4x=3,y=4

Explanation:

Given: 8x-9y=128x9y=12. Solve for x.
8x-9y+9y=12+9y8x9y+9y=12+9y
8x=12+9y8x=12+9y
(8x)/8=(12+9y)/88x8=12+9y8

x=(12+9y)/8x=12+9y8

Substitute this into the other equation:

-8x+3y=128x+3y=12

-8((12+9y)/8)+3y=128(12+9y8)+3y=12

-1(12+9y)+3y=121(12+9y)+3y=12

-12-9y+3y=12129y+3y=12

-12-6y=12126y=12

-12-6y+12=12+12126y+12=12+12

-6y=246y=24

(-6y)/-6=24/-66y6=246

y=-4y=4

Substitute into original equation:

8x-(9*-4)=128x(94)=12

8x+36=128x+36=12

8x+36-36=12-368x+3636=1236

8x =-248x=24

(8x)/8=-24/88x8=248

x=-3x=3

To check, substitute both answers into both the formulas:

-8*-3+3*-4=24-12=1283+34=2412=12 True

8*-3-9*-4=-24+36=128394=24+36=12 True