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WAEC Mathematics 2006 Question 29

Question 29

Graphs of Functions

Use the graphs to answer this question. What is the equation of the curve?

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

Answer: B (y = 3 − 2x − x2)

Explanation

The curve cuts the x-axis at x = −3 and x = 1 and turns at the top, so y = −(x + 3)(x − 1) = 3 − 2x − x2. Check: at x = −1, y = 3 + 2 − 1 = 4, the highest point on the graph.