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JAMB Mathematics 1999 Question 14

Question 14

Binary Operations

A binary operation ∗ is defined by a∗b = ab + a + b for any real number a and b. If the identity element is zero, find the inverse of 2 under this operation.

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

Answer: D (−2/3)

Explanation

The inverse b satisfies 2∗b = 0: 2b + 2 + b = 0, so 3b = −2 and b = −2/3.