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JAMB Mathematics 2007 Question 23

Question 23

Binary Operations

A binary operation Δ is defined by aΔb = a + b + 1 for any real numbers a and b. Find the inverse of the real number 7 under the operation Δ, if the identity element is −1.

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

Answer: B (−9)

Explanation

7 Δ a−1 must equal the identity: 7 + a−1 + 1 = −1, so a−1 = −9.