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-x-y=-9

-3x-2y=-28

eliminate the x first

multiply the first system of equations by 3

(3)(-x)=-3x

(3)(-y)=-3y

(3)(-9)=-27

-3x-3y=-27

-3x-2y=-28

eliminate the systems of equations by subtracting

-3x--3x-3y--2y=-27--28

-3x+3x-3y+2y=-27+28

-y=1

multiply -1 for -y=-1  to get positive y

(-y)(-1)=(1)(-1)

y=-1

substitution method by using y=-1 into one of the system of equations

-x-y=-9

-x--1=-9

-x+1=-9

move +1 to the other side

sign changes from +1 to -1

-x+1-1=-9-1

-x=-10

multiply by -1 for -x=-10 to get positive x

(-x)(-1)=(-10)(-1)

x=10

x=10, y=-1  

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