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JAMB Mathematics 2014 Question 21

Question 21

Binary Operations

A binary operation * is defined by x * y = xy. If x * 2 = 12 − x, find the possible values of x.

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

Answer: C (3, −4)

Explanation

x * 2 = x2, so x2 = 12 − x, i.e. x2 + x − 12 = 0 = (x − 3)(x + 4). So x = 3 or −4.