SOLUTION: Determine the cubic function f(x) in factored form with integral coefficients, such that it has the following properties, 1) the third differences are equal to 18 2) the remainde

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Question 1186359: Determine the cubic function f(x) in factored form with integral coefficients, such that it has the following properties,
1) the third differences are equal to 18
2) the remainder f(x)/(x-2) is 27
3) x+1 is a factor
4) (1,6) is a point on f(x)

Answer by greenestamps(13208) About Me  (Show Source):
You can put this solution on YOUR website!


(1) For a cubic polynomial, the third differences are constant, and that constant third difference is 3!=6 times the leading coefficient. With a constant difference of 18, the leading coefficient of f(x) is 3.

(2) If the remainder when f(x) is divided by (x-2) is 27, then f(2)=27.

(3) We are given that one of the factors is (x+1).

(4) (1,6) is a point on the graph of f(x) means f(1)=6.

From the given information, we know f(x) has the following factored (possibly only partially factored) form:

f%28x%29=%283%29%28x%2B1%29%28x%5E2%2Bbx%2Bc%29

f%282%29=%283%29%283%29%284%2B2b%2Bc%29+=+9%284%2B2b%2Bc%29+=+27
4%2B2b%2Bc=27%2F9+=+3
2b%2Bc=-1 [1]

f%281%29=%283%29%282%29%281%2Bb%2Bc%29=6%281%2Bb%2Bc%29=6
1%2Bb%2Bc=1
b%2Bc=0 [2]

Solving [1] and [2] together finds b = -1 and c = 1.

So the quadratic factor is x%5E2-x%2B1, which does not factor over the integers. So

ANSWER: f%28x%29+=+%283%29%28x%2B1%29%28x%5E2-x%2B1%29