If * is a binary operation on Z such that a * b = a + b + 1 ∀ a, b ∈ Z then find the identity element of Z with respect to * ?

  1. -1
  2. 1
  3. 0
  4. None of these

Answer (Detailed Solution Below)

Option 1 : -1
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Detailed Solution

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Concept:

Let * be a binary operation on a non-empty set S. If there exists an element e in S such that a * e = e * a = a ∀ a ∈ S. Then the element e is said to be an identity element of S with respect to *.

Calculation:

Given: * is a binary operation on Z such that a * b = a + b + 1 ∀ a, b ∈ Z.

Let e be the identity element of Z with respect to *.

As we know that if e is an identity element of a non-empty set S with respect to a binary operation * then a * e = e * a = a ∀ a ∈ S.

Let a ∈ Z and because e is the identity element of Z with respect to given operation *.

i.e a * e = a =  e * a ∀ a ∈ Z.

According to the definition of *, we have

⇒ a * e = a + e + 1 = a ∀ a ∈ Z

⇒ e = - 1

Hence, - 1 is the identity element of Z with respect to given operation *.

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