A binary operation is defined by a b a b 1 for ... - JAMB Mathematics 2007 Question
A binary operation Δ is defined by aΔb = a + b + 1 for any numbers a and b. Find the inverse of the real number 7 under the operation Δ, if the identity element is -1
A
-7
B
-9
C
5
D
9
correct option: b
a*e = a + e + 1 = a
implies e+ 1 = 0
∴ e = -1
7 * e = -1
∴ a + 7 + 1 = -1
a + 8 = -1
a+8 = -1
a = -1-8
a = -9
implies e+ 1 = 0
∴ e = -1
7 * e = -1
∴ a + 7 + 1 = -1
a + 8 = -1
a+8 = -1
a = -1-8
a = -9
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