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JAMB Mathematics 1992 Question 21

Question 21

Binary Operations

If the binary operation * is defined by m * n = mn + m + n for any real number m and n, find the identity element e under the operation

  1. A.e = 1
  2. B.e = −1
  3. C.e = −2
  4. D.e = 0
Show the answer and explanation

Answer: D (e = 0)

Explanation

We need m * e = m: me + m + e = m, so e(m + 1) = 0 for every m. Hence e = 0.