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Question 147516: I had help with a previous question, and it was not a solvable problem. I need to see the steps on how the elimination process is done. Could you please help?
7r-4s=7
4r+7s=69
I need to solve using the elimination method. I think I need to solve for x, and use that answer in the 2nd equation. Your help is greatly apprecieated.
Answer by Alan3354(69443)   (Show Source):
You can put this solution on YOUR website! 7r-4s=7 eqn 1
4r+7s=69 eqn 2
This is 2 equations in 2 unknowns, r and s. You can solve for both r and s.
To eliminate one of the variables, you multiply both eqns by a number that will give the same coefficient for one of the variables. This is similar to finding the LCD, Least Common Denominator.
To eliminate the r terms, multiply eqn 1 by 4 and eqn 2 by 7.
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28r - 16s = 28
28r + 49s = 483
Subtract (2) from (1)
0r - 65s = -455
s = 7
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Substitute s into either eqn to find r.
7r -4*7 = 7
7r = 35
r = 5
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Check both eqns.
7*5 - 4*7 = 7 so eqn 1 is good.
4*5 + 7*7 = 69 so they both check.
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