SOLUTION: Solve the system of equations where x + 4y = 7 and 3x + y = -1

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Question 1070146: Solve the system of equations where x + 4y = 7 and 3x + y = -1
Found 3 solutions by Boreal, Fombitz, Edwin McCravy:
Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
x + 4y = 7 and 3x + y = -1
x=7-4y
3(7-4y)+y=-1
21-12y+y=-1
-11y=-22
y=2
x=7-4(2)=-1
(-1, 2)
check in second equation
-3+2=-1
this was done by substitution, but it can be done by elimination as well.
multiply top by -3
-3x-12y=-21
3x+y=-1
-11y=-22
y=2

Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
From the second equation,
y=-1-3x
Substitute into the first,
x%2B4%28-1-3x%29=7
x-4-12x=7
-11x=11
x=-1
Now use either equation to solve for y

Answer by Edwin McCravy(20055) About Me  (Show Source):
You can put this solution on YOUR website!
Unlike the others, I'd rather not just do your work for you
all the time.  So I like to do one just like it, and let you
do your own work.  But before I had finished they had already
done it for you.

Here's one exactly like it

system%28x+%2B+5y+=+13%2C4x+%2B+y+=+-5%29

Solve either equation for either letter.
I'll solve the first equation for x

x + 5y = 13
  - 5y   -5y
------------
     x = 13-5y

Substitute (13-5y) for x in the other equation:

       4x + y = -5
 4(13-5y) + y = -5  
 52 - 20y + y = -5
     52 - 19y = -5
    -52         -52
  ----------------
         -19y = -57
           y = (-57)/(-19)
           y = 3

Substitute (3) for y in

     x = 13-5y
     x = 13-5(3)
     x = 13-15
     x = -2

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

Now do your exactly the same way, step by step.

Edwin