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Regarding the function \(f(x)=x^{2}-5 x+1\) and \(g(x)=1-x-x^{3}\) on the set of real numbers, which of the following statements is NOT true?

Question and options

Regarding the function f(x)=x2−5x+1f(x)=x^{2}-5 x+1 and g(x)=1−x−x3g(x)=1-x-x^{3} on the set of real numbers, which of the following statements is NOT true?
  1. The graph of ff and gg intersect at three different points.
  2. The graph of ff and gg intersect at just one point with positive abscissa.
  3. The graph of ff and gg intersect at just one point with negative abscissa.
  4. The graph of ff and gg intersect at just one point with a positive yy-coordinate.

Answer and explanation

Correct answer: D - The graph of \(f\) and \(g\) intersect at just one point with a positive \(y\)-coordinate.
f = g gives x^3 + x^2 - 4x = 0, x = 0, (-1 +/- sqrt17)/2 ~ 1.56, -2.56: three points, one with positive and one with negative abscissa. y-values: f(0)=1>0, f(-2.56)~20.4>0, f(1.56)~-4.4<0, so two intersection points have a positive y-coordinate; the claim that just one does is false.

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