MATHEMATICS

JAMB 2005 - Question 21

Mathematics 2005 JAMB Past Questions - Question 21: An operation *is defined on the set of real numbers . by a* b = ab + 2 (a + b + 1).Find the identity element .

Choose the most appropriate option for the gap .
An operation *is defined on the set of real numbers . by a* b = ab + 2 (a + b + 1).Find the identity element .
A:
B:
C:
D:
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Correct Answer

C

Explanation

a * b = ab + 2(a + b + 1)let e be the identity element∴ a * e = e * a = a∴ a * e = aae + 2(a + e + 1) = aae + 2a + 2e + 2 = aae + 2e = a - 2a = 2(a + 2)e = -a - 2e = -a-2 / (a+2)e = -(a+2) / (a+2)e = -1