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Question 248015: 5r-4s= -6 and 4r+5s=69
Answer by oberobic(2304)   (Show Source):
You can put this solution on YOUR website! 5r - 4s = -6
4r + 5s = 69
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Subtract the second equation from the first
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r - 9s = -75
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Add 9s to both sides.
r = 9s - 75
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Substitute
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4r + 5s = 69
4(9s - 75) + 5s = 69
36s - 300 + 5s = 69
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Add 300 to both sides
36s + 5s = 300 + 69
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Collect terms.
41s = 369
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Divide both sides by 41.
s = 369/41 = 9
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Substitute into the other equation.
4r + 5(9) = 69
4r + 45 = 69
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Subtract 45 from both sides.
4r = 24
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Divide both sides by 4.
r = 6
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So, we have the candidate answer is:
s = 9
r = 6
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Check by substituting the values into the original equations.
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5r - 4s = -6
5r = 30
4s = 36
5r - 4s = -6
OK
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4r + 5s = 69
4r = 24
5s = 45
4r + 5s = 69
OK
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