Question 108984
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<font size = 6 color = red>WARNING: FOMBITZ' SOLUTION IS INCORRECT.
CORRECT SOLUTION BY EDWIN:</font>
<pre><font size = 4><b>
Solve each of the following systems by graphing.

 x - 2y =  8
3x - 2y = 12

Get two points on the first line.
Plot them and draw a line through them.
Get two points on the second line.
Plot them and draw a line through them.
Identify the coodinates of the point where the two lines cross.

Get two points on the first line whose equation is  x - 2y =  8

Arbitrarily pick any convenient number to substitute
for either letter.  I think I will first choose 0 to substitute
for x.  I chose 0 simply because it is easy.  I could have chosen
any other number, and for either letter.  So we substitute x = 0

 x - 2y = 8
 0 - 2y = 8
    -2y = 8
      y = {{{8/(-2)}}} 
      y = -4, so one point on the first line is (x, y) = (0,-4) 

Now for the second point on the first line, I think I will choose 0 to substitute for y.  Again I chose 0 simply because it is easy.  I could 
have chosen any other number, and for either letter.  So we substitute
y = 0

   x - 2y = 8
 x - 2(0) = 8
    x - 0 = 8
        x = 8, so another point on the first line is (x, y) = (8, 0)

Plot the two points (0, -4) and (8, 0):

{{{drawing(400,375,-10,10,-10,10,
   locate(7.8,0.5,X), locate(7.8,0.5,O),
locate(7.8,0.5,W), locate(7.8,0.5,M), 
   locate(-.2,-3.55,X), locate(-.2,-3.55,O),
locate(-.2,-3.55,W), locate(-.2,-3.55,M),

   graph(400,375,-10,10,-10,10) )}}} 

Draw a straight line through them:

{{{drawing(400,375,-10,10,-10,10,
   locate(7.8,0.5,X), locate(7.8,0.5,O),
locate(7.8,0.5,W), locate(7.8,0.5,M), 
   locate(-.2,-3.55,X), locate(-.2,-3.55,O),
locate(-.2,-3.55,W), locate(-.2,-3.55,M),

   graph(400,375,-10,10,-10,10,(8-x)/(-2)) )}}} 

Get two points on the second line, whose equation is 3x - 2y = 12

Arbitrarily pick any convenient number to substitute
for either letter.  I will again first choose 0 to substitute
for x.  Again I chose 0 simply because it is easy.  I could have chosen
any other number, and for either letter.  So we substitute x = 0

  3x - 2y = 12
3(0) - 2y = 12
      -2y = 12
      y = {{{12/(-2)}}} 
      y = -6, so one point on the second line is (x, y) = (0,-6) 

Now for the second point on the second line, I will again choose 0 to
substitute for y.  Again I chose 0 simply because it is easy.  I could 
have chosen any other number, and for either letter.  So we substitute
y = 0

  3x - 2y = 12
3x - 2(0) = 12
   3x - 0 = 12
       3x = 12
        x = {{{12/3}}}
        x = 4

so another point on the second line is (x, y) = (4, 0)

Plot the two points (0, -6) and (4, 0):

{{{drawing(400,375,-10,10,-10,10,
   locate(7.8,0.5,X), locate(7.8,0.5,O),
locate(7.8,0.5,W), locate(7.8,0.5,M), 
   locate(-.2,-3.55,X), locate(-.2,-3.55,O),
locate(-.2,-3.55,W), locate(-.2,-3.55,M),

   locate(3.8,0.5,X), locate(3.8,0.5,O),
locate(3.8,0.5,W), locate(3.8,0.5,M), 
   locate(-.2,-5.55,X), locate(-.2,-5.55,O),
locate(-.2,-5.55,W), locate(-.2,-5.55,M),

   graph(400,375,-10,10,-10,10,(8-x)/(-2))  )}}} 

Draw a straight line through them:

{{{drawing(400,375,-10,10,-10,10,
   locate(7.8,0.5,X), locate(7.8,0.5,O),
locate(7.8,0.5,W), locate(7.8,0.5,M), 
   locate(-.2,-3.55,X), locate(-.2,-3.55,O),
locate(-.2,-3.55,W), locate(-.2,-3.55,M),
   locate(3.8,0.5,X), locate(3.8,0.5,O),
locate(3.8,0.5,W), locate(3.8,0.5,M), 
   locate(-.2,-5.55,X), locate(-.2,-5.55,O),
locate(-.2,-5.55,W), locate(-.2,-5.55,M),
   graph(400,375,-10,10,-10,10,(8-x)/(-2)), 
   graph(400,375,-10,10,-10,10,(12-3x)/(-2))
)}}} 

To identify the coodinates of the point where the 
two lines cross, draw both a horizontal line and
a vertical line through that point. These are the
green lines below:

{{{drawing(400,375,-10,10,-10,10,
   locate(7.8,0.5,X), locate(7.8,0.5,O),
locate(7.8,0.5,W), locate(7.8,0.5,M), 
   locate(-.2,-3.55,X), locate(-.2,-3.55,O),
locate(-.2,-3.55,W), locate(-.2,-3.55,M),
   locate(3.8,0.5,X), locate(3.8,0.5,O),
locate(3.8,0.5,W), locate(3.8,0.5,M), 
   locate(-.2,-5.55,X), locate(-.2,-5.55,O),
locate(-.2,-5.55,W), locate(-.2,-5.55,M),
   graph(400,375,-10,10,-10,10,(8-x)/(-2),-3), 
   graph(400,375,-10,10,-10,10,(12-3x)/(-2),999(x-2))
)}}}

Notice that the vertical green line goes through 2 on
the x-axis, and the horizontal one goes through -3 on
the y-axis, so the solution is 

(x, y) = (2,-3)

We now check to see if we are correct. 
First we substitute x = 2, and y = -3 into the first
equation to see if we get a true statement:

   x - 2y = 8
2 - 2(-3) = 8
    2 + 6 = 8
        8 = 8

That is true, but to completely check the problem
we must also substitute x = 2, and y = -3 into the second
equation to see if we also get a true statement.

     3x - 2y = 12
3(2) - 2(-3) = 8
       6 + 6 = 12
          12 = 12

That is true also, so (x, y) = (2, -3) is the correct
solution to the system.

Edwin</pre>