SOLUTION: For the given rational function f, find all values of x for which f(x) has the indicated value. f(x) = 5x + 21/x ; f(x) = -38

Algebra ->  Expressions-with-variables -> SOLUTION: For the given rational function f, find all values of x for which f(x) has the indicated value. f(x) = 5x + 21/x ; f(x) = -38      Log On


   

Question 203772: For the given rational function f, find all values of x for which f(x) has the indicated value.
f(x) = 5x + 21/x ; f(x) = -38
Answer by RAY100(1637) About Me  (Show Source):
You can put this solution on YOUR website!
f(x) = -38 = 5x +21/x
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mult thru by x
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-38x = 5x^2 +21
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0=5x^2 +38x +21
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factor
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(5x+3)(x+7) =0
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x= -3/5,,,-7
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check
(-7),,,-38=5(-7) +21/(-7)
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-38 = -35 -3,,,,,,ok
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(-3/5),,,,,-38 =5(-3/5) + 21/(-3/5)
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-38 = -3 -35 = -38,,,,,ok