passpadi

2012

Mathematics

JAMB

The binary operation on the set of real numbers is defined by m*n = mn/2 for all m, n ∈ R. If the identity element is 2, find the inverse of -5

A.

−4/5

B.

−2/5

C.

4

D.

5

Correct Answer: −4/5

Explanation

m * n = mn/2 Identify, e = 2 Let a ∈ R, then a * a-1 = e a * a-1 = 2 -5 * a-1 = 2 −5×a-1 /2 = 2 a-1 = 2 × 2/−5 a-1 = −4/5

m * n = mn/2 Identify, e = 2 Let a ∈ R, then a * a-1 = e a * a-1 = 2 -5 * a-1 = 2 −5×a-1 /2 = 2 a-1 = 2 × 2/−5 a-1 = −4/5
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