SOLUTION: Use the substitution method to solve each system and provide the coordinates. I've got most of them, but these ones I keep getting wrong. Can someone help please? (1) {{{3x-2y=3

Algebra ->  Linear-equations -> SOLUTION: Use the substitution method to solve each system and provide the coordinates. I've got most of them, but these ones I keep getting wrong. Can someone help please? (1) {{{3x-2y=3      Log On


   



Question 104455: Use the substitution method to solve each system and provide the coordinates. I've got most of them, but these ones I keep getting wrong. Can someone help please?
(1) 3x-2y=33%2F2 and x%2F2-11%2F4=2y
(2) 4x%2B5y%2B1=-10%2B2x and x-3y%2B2=-1-x This is not (3,1). :(
(3) r%2B3s=15 and 3r%2B2s=17 This should be the easiest, but it's not (3,4)
Thanks so much!

Answer by Edwin McCravy(20056) About Me  (Show Source):
You can put this solution on YOUR website!
Use the substitution method to solve each system and provide the coordinates. I've got most of them, but these ones I keep getting wrong. Can someone help
please?

(1) 3x-2y=33%2F2
    x%2F2-11%2F4=2y

First clear them both of fractions.  To clear the first equation of
fractions multiply every term by the LCD of 2

2%283x%29-2%282y%29+=+2%2833%2F2%29

which simplifies to

6x+-+4y+=+33 which has no fractions.

To clear the second equation of
fractions multiply every term by LCD of 4

4%28x%2F2%29-4%2811%2F4%29=4%282y%29

which simplifies to

2x+-+11+=+8y which has no fractions

So now the system of equations to solve is:

6x+-+4y+=+33
2x+-+11+=+8y

Rearranging the second equation like the
first equation

6x+-+4y+=+33
2x+-+8y+=+11

To make the y's cancel out, multiply the
first equation through by -2

            6x+-+4y+=+33
%28-2%29%286x%29+-+%28-2%29%284y%29+=+%28-2%29%2833%29
which simplifies to
          -12x+%2B+8y+=+-66

Now place the second equation directly under
this:

-12x+%2B+8y+=+-66
 +2x+-+8y+=+11

Adding term by term gives

-12x+%2B+8y+=+-66
 +2x+-+8y+=+11
--------------------
     -10x+=+-55
        x+=+%28-55%29%2F%28-10%29
        x+=+55%2F10
        x+=+11%2F2

To make the x's cancel out, multiply the
second equation through by -3.

6x+-+4y+=+33
2x+-+8y+=+11

%28-3%29%282x%29+-+%28-3%29%288y%29+=+%28-3%29%2811%29

-6x+%2B+24y+=+-33

Now place this equation directly under the
first equation:

 6x+-++4y+=++33
-6x+%2B+24y+=+-33

Adding term by term gives

 6x+-++4y+=++33
-6x+%2B+24y+=+-33
--------------------
      20y+=+0
        y+=+0%2F20
        y+=+0
       
So the solution is (x,y) = (11%2F2,0)      

============================================= 

(2) 4x%2B5y%2B1=-10%2B2x
    x-3y%2B2=-1-x  

Rearrange the terms of the first equation as 2x%2B5y=-11
Rearrange the terms of the second equation as -2x-3y=-1

 2x%2B5y=-11
-2x-3y=-1

The x's will cancel as they are:

Add term by term:

 2x%2B5y=-11
-2x-3y=-1
-----------------
       2y=-12
     y=%28-12%29%2F2 
     y=-6

Substitute -6 for y in the 1st equation:

    2x%2B5y=-11
 2x%2B5%28-6%29=-11
    2x-30=-11
       2x+=+19 
        x+=+19%2F2

So the solution is (x,y) = (19%2F2,-6)

=======================================

(3)  r%2B3s=15
    3r%2B2s=17 

To make the r's cancel, multiply the
first equation by -3

            r%2B3s=15
%28-3%29%28r%29%2B%28-3%29%283s%29=%28-3%29%2815%29
          -3r-9s=-45
          
Now write the second equation under this:
 
          -3r-9s=-45
           3r%2B2s=17 
        
Add term by term:

          -3r-9s=-45
           3r%2B2s=17
         ------------------
             -7s=-28
               s=%28-28%29%2F%28-7%29  
               s=4

Substitute 4 for s in 
            r%2B3s=15     
          r%2B3%284%29=15
            r%2B12=15
               r=3

So the solution is (r,s) = (3,4). So
yes it it is (3,4)!

Edwin