passwella.
Menu

JAMB Mathematics 2005 Question 21

Question 21

Binary Operations

An operation * is defined on the set of real numbers by a * b = ab + 2(a + b + 1). Find the identity element.

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

Answer: C (−1)

Explanation

a * e = a gives ae + 2a + 2e + 2 = a, so e(a + 2) = −(a + 2) and e = −1.