Where am I going wrong on this solution?

Question

2x-y= -6

x+y= -6

 

started with x+y= -6

x=-6 - y

 

then

2( -6-y) -y = -6

-12-2y-y= -6

-12-3y=-6

-3y= -18

y= -6

 

x+ -6=-6

x=0

 

so I have the ordered pair as (0, -6)

 

is this correct?

Answer 1

 To find out test your answer. 

 

   It doesn't work.

 

    Your error is :

 

     - 12 - 3Y = -6 

 

       -3Y = 6     / You have it @ - 18 

 

        

Answer 2

You have:

-12-3y=-6
-3y= -18

You added 12 to the left but subtracted 12 from the right.

To guard against this error use a "change" equation.

-12-3y=-6
+12 = +12 <== "change" equation
–––––––––
0 - 3y = +6

y = -2

x + (-2) = -6
+ 2 = + 2
–––––––––––––
x + 0 = -4

Solution is (-4,-2)