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GCE Mathematics 1989 Question 19

Question 19

Quadratic Equations

If 5 times a certain integer is subtracted from twice the square of the integer, the result is 63. Find the integer.

  1. A.21
  2. B.9
  3. C.7
  4. D.4
  5. E.3
Show the answer and explanation

Answer: C (7)

Explanation

2n2 − 5n = 63 gives 2n2 − 5n − 63 = (2n + 9)(n − 7) = 0. The integer is 7.