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JAMB Mathematics 2004 Question 11

Question 11

Graphs of Functions

Find the values of x where the curve y = x3 + 2x2 − 5x − 6 crosses the x-axis

  1. A.−2, −1 and 3
  2. B.−2, 1 and −3
  3. C.2, −1 and −3
  4. D.2, 1 and 3
Show the answer and explanation

Answer: C (2, −1 and −3)

Explanation

x = 2 makes the cubic zero, and dividing by (x − 2) leaves x2 + 4x + 3 = (x + 1)(x + 3). So x = 2, −1, −3.