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WAEC Mathematics 1995 Question 21

Question 21

Graphs of Functions

Use the graph of y = 3x2 + x − 7 to answer this question. Find the roots of the equation y = 3x2 + x − 7

Diagram for this question
  1. A.1.0 and −1.2
  2. B.1.1 and −1.3
  3. C.1.4 and −1.7
  4. D.2.0 and −1.9
  5. E.2.4 and −2.0.
Show the answer and explanation

Answer: C (1.4 and −1.7)

Explanation

The roots are where the curve cuts the x-axis: about x = 1.4 and x = −1.7 (the formula gives (−1 ± √85)/6).