A binary operation defined on the set of intege... - JAMB Mathematics 2009 Question
A binary operation ⊗ defined on the set of integers is such that m⊗n = m + n + mn for all integers m and n. Find the inverse of -5 under this operation, if the identity element is 0
A
-5/4
B
-5/6
C
zero
D
5
correct option: a
m⊗n = m + n + mn
for inverse -5-1 x -5 = e
-5-1 + -5 + (-5-1)(-5) = 0
-5 + (-5-1(-5)) = 5
-5-1.(1 + -5) = 5
-5-1(-4) = 5
-5-1 = -5/4
for inverse -5-1 x -5 = e
-5-1 + -5 + (-5-1)(-5) = 0
-5 + (-5-1(-5)) = 5
-5-1.(1 + -5) = 5
-5-1(-4) = 5
-5-1 = -5/4
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