2000 AMC 12 Problems/Problem 22

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Problem

The graph below shows a portion of the curve defined by the quartic polynomial $P(x) = x^4 + ax^3 + bx^2 + cx + d$. Which of the following is the smallest?

$\text{(A)}\ P(-1)\\ \text{(B)}\ \text{The\ product\ of\ the\ zeros\ of\ } P\\ \text{(C)}\ \text{The\ product\ of\ the\ non-real\ zeros\ of\ } P \\ \text{(D)}\ \text{The\ product\ of\ the\ coefficients\ of\ } P \\ \text{(E)}\ \text{The\ product\ of\ the\ real\ zeros\ of\ } P$


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Solution

We note that there are no more zeros of this polynomial, as there already have been three turns in the curve. We approximate each of the above expressions:

  1. According to the graph, $P(-1) > 4$
  2. The product of the roots is $d$ by Vieta’s formulas. Also, $d = P(0) > 5$ according to the graph.
  3. The product of the real roots is $>5$, and the total product is $<6$ (from above), so the product of the non-real roots is $< \frac{6}{5}$.
  4. The sum of the coefficients is $P(1) > 1.5$
  5. The sum of the real roots is $> 5$.

Clearly $\mathrm{(C)}$ is the smallest.

See also

2000 AMC 12 (ProblemsAnswer KeyResources)
Preceded by
Problem 20
Followed by
Problem 22
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
All AMC 12 Problems and Solutions
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