Mathematics
JAMB 2008
A binary operation * is defined on the set of positive integers is such x*y = 2x-3y+2 for all positive integers x and y. The binary operation is?
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A.
commutative and close on the set of positive integers
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B.
neither commutative nor closed on the set of positive integers
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C.
commutative but not closed on the set of positive integers
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D.
not cummutative but closed on the set of positive integers
Correct Answer: Option B
Explanation
X * Y = 2X - 3Y + 2
2*3 = 2(2) - 3(3) + 2
=4-9+2
= -3
But -3 does not belong to positive integer
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