Question 203720
f(6)  =-1
f(3) =8
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Let  f(x) = cx +k
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(1) f(6) =6c +k = -1
(2) f(3) = 3c +k = 8
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substract  (1) - (2)
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3c =-9,,,,c=-3
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subst (2),,,,3(-3) +k =8
k=17
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f(x) = -3x +17
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check, f(6) = -3(6) +17 = -1,,,,,ok
f(3) = -3(3) +17 = 8,,,,ok