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JAMB Mathematics 1984 Question 18

Question 18

Graphs of Functions

The table below is drawn for a graph y = x3 − 3x + 1
x: −3, −2, −1, 0, 1, 2, 3
y: 1, −1, 3, 1, −1, 3, 1
From x = −2 to x = 1, the graph crosses the x-axis in the range(s)

  1. A.−1 < x < 0 and 0 < x < 1
  2. B.−2 < x < −1 and 0 < x < 1
  3. C.−2 < x < −1 and −1 < x < 0
  4. D.0 < x < 1
  5. E.1 < x < 2.
Show the answer and explanation

Answer: B (−2 < x < −1 and 0 < x < 1)

Explanation

y changes sign between x = −2 (−1) and x = −1 (3), and between x = 0 (1) and x = 1 (−1). So the graph crosses the x-axis in −2 < x < −1 and 0 < x < 1.