Question 18

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Jambmaths question: 

An operation *is defined on the set of real numbers by a * b  = a + b + 1. If the identity element is –1 . Find the inverse of the element 2 under the operation

Option A: 

4

Option B: 

0

Option C: 

–2

Option D: 

–4

Jamb Maths Solution: 

$\begin{align}  & a*b=a+b+1 \\ & a*{{a}^{-1}}=e\text{    }\!\!\{\!\!\text{ }where {{a}^{-1}} is the inverse of a, e=identity element\} \\ & 2*{{2}^{-1}}=-1 \\ & 2*{{2}^{-1}}=2+{{2}^{-1}}+1=-1 \\ & 2+{{2}^{-1}}+1=-1 \\ & {{2}^{-1}}=-1-3 \\ & {{2}^{-1}}=-4 \\\end{align}$The inverse of 2 is –4 

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