SOLUTION: Use elimination to solve each system of equations. I have to show all work and write the answer as an (x,y) ordered. 7x+4y=-4 5x+8y=28

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Question 1056580: Use elimination to solve each system of equations. I have to show all work and write the answer as an (x,y) ordered.
7x+4y=-4
5x+8y=28
Found 2 solutions by ikleyn, ankor@dixie-net.com:
Answer by ikleyn(52794)   (Show Source): You can put this solution on YOUR website!
.
Use elimination to solve each system of equations. I have to show all work and write the answer as an (x,y) ordered.
7x+4y=-4
5x+8y=28
~~~~~~~~~~~~~~~~~ 

7x + 4y = -4,      (1)
5x + 8y = 28.      (2)

Multiply equation (1) by 5 (both sides).
Multiply equation (2) by 7 (both sides). You will get

35x + 20y = -20,   (1')
35x + 56y = 196.   (2')

Distract (1) from (2) (both sides). You will get

56y - 20y = 196 - (-20),   (<--- you got a single equation for only one unknown. It is how ELIMINATION method works !)

36y = 216,

y =  = 6.

Thus you just found "y".

Then from (1) 7x = -4 - 4y = -4 -4*6 = -28.

x =  = -4.

Answer.  x = -4,  y = 6.

On Elimination method see the lesson
    - Solution of a linear system of two equations in two unknowns by the Elimination method
in this site.


Answer by ankor@dixie-net.com(22740)   (Show Source): You can put this solution on YOUR website!
7x + 4y =-4
5x + 8y = 28
:
Multiply the first equation by -2, add the 2nd equation
-14x - 8y = 8
5x + 8y = 28
-----------------
-9x = 36
x = 36/-9
x = -4
Find y using the 1st equation; replace x with -4
7(-4) + 4y = -4
-28 + 4y = -4
4y = -4 + 28
4y = 24
y = 24/4
y = 6
:
:
Check solutions in the 2nd equation; replace x and y
5(-4) + 8(6) = 28
-20 + 48 = 28
:
-4,6
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