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JAMB Mathematics 1979 Question 47

Question 47

Quadratic Equations

If y = x2 − 2x − 3, find the least value of y and the corresponding value of x

  1. A.x = 3, y = −3
  2. B.x = 1, y = −3
  3. C.x = −4, y = 1
  4. D.x = 1, y = −4
  5. E.x = 2, y = −3.
Show the answer and explanation

Answer: D (x = 1, y = −4)

Explanation

y = (x − 1)² − 4, which is smallest when x = 1, giving y = −4.