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Last updated at Jan. 28, 2020 by Teachoo

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Misc 13 Given a non-empty set X, let *: P(X) × P(X) → P(X) be defined as A * B = (A − B) ∪ (B − A), ∀ A, B ∈ P(X). Show that the empty set ϕ is the identity for the operation * and all the elements A of P(X) are invertible with A−1 = A. (Hint: (A − ϕ) ∪ (ϕ – A) = A and (A − A) ∪ (A − A) = A * A = ϕ). Identity e is the identity of * if a * e = e * a = a Here, A * ϕ = (A − ϕ) ∪ (ϕ – A) = A ∪ ϕ = A & ϕ * A = (ϕ − A) ∪ (A – ϕ) = ϕ ∪ A = A Since, A * ϕ = ϕ * A = A 𝛟 is the identity of operation * Invertible An element a in set is invertible if, there is an element in set such that , a * b = e = b * a Here, e = ϕ , b = A Now, A * A = (A − A) ∪ (A – A) = ϕ ∪ ϕ = ϕ & A * A = (A − A) ∪ (A – A) = ϕ ∪ ϕ = ϕ Since, A * A = ϕ = A * A Hence, all the elements A of P(X) are invertible with inverse of A = A

Binary operations: Inverse

Chapter 1 Class 12 Relation and Functions

Concept wise

- Relations - Definition
- Empty and Universal Relation
- To prove relation reflexive, transitive, symmetric and equivalent
- Finding number of relations
- Function - Definition
- To prove one-one & onto (injective, surjective, bijective)
- Composite functions
- Composite functions and one-one onto
- Finding Inverse
- Inverse of function: Proof questions
- Binary Operations - Definition
- Whether binary commutative/associative or not
- Binary operations: Identity element
- Binary operations: Inverse

About the Author

Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 9 years. He provides courses for Maths and Science at Teachoo.