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JAMB Mathematics 2007 Question 17

Question 17

Graphs of Functions

The graph above is represented by

Diagram for this question
  1. A.y = x3 − 3x − 2
  2. B.y = x3 + 2x2 − x − 2
  3. C.y = x3 − 4x2 + 5x − 2
  4. D.y = x3 − 4x + 2
Show the answer and explanation

Answer: B (y = x3 + 2x2 − x − 2)

Explanation

The curve cuts the x-axis at −2, −1 and 1, so y = (x + 2)(x + 1)(x − 1) = x3 + 2x2 − x − 2, which also gives y = −2 at x = 0 as on the graph.