The words ‘element’, ‘object’, and ‘member’ are synonymous.

**Sets designated by specific letters.**

N: natural numbers

Z : integers

Z+: positive integers

Q: rational numbers

Q+: positive rational numbers

R: real numbers

R+: positive real numbers

C: complex numbers

Description of a set

Sets can be described by roster method or set-builder method.

Types of sets

Empty set

Singleton set

Finite set

Infinite set

Equivalent set

Equal set

Subset

Universal set

Power set

Theorems on subsets

1. Every set is a subset of itself.

2. The empty set is a subset of every set.

3. The total number of subsets of a finite set containing n elements is 2ⁿ

Laws of algebra of sets

1. Idempotent laws

(i) A U A = A

(ii) A ∩ A = A

2. Identity laws

(i) A U ф = A

(ii) A ∩ U = A

3. commutative law

(i) A U B = B U A

(ii) A ∩ B = B ∩ A

4. Associative laws

(i) (A U B) U C = A U (B U C)

(ii) (A ∩ B) ∩ C = A ∩ (B ∩ C)

5. Distributive laws

(i) A U (B ∩ C) = (A U B) ∩ (A U C)

(ii) A ∩ (B U C) = (A ∩ B) U (A ∩ C)

6. De-morgan’s laws

(i) (A U B)’ = A’ ∩ B’

(ii) (A ∩ B)’ = A’ U B’

Some more theorems

If A and B are two sets

(i) A – B = A ∩ B’

(ii) B – A = B ∩ A’

(iii) A – B = A A ∩ B = ф

(iv) (A – B) U B = A U B

(v) (A-B) ∩ B = ф

(vi) A is a sub set of B B’ is a subset of A’

(vii) (A-B) U (B-A) = (A U B) – (A ∩ B)

If A, B and C are three sets, then

(i) A – (B ∩ C) = (A-B) U (A-C)

(ii) A – (B U C) = (A-B) ∩ (A-C)

(iii) A ∩ (B-C) = (A ∩ B) - (A ∩ C)

(iv) A ∩ (B Δ C) = (A∩B) Δ (A∩C)

Some results on Number of elements in sets n(A), n(B), and n(C)

Note union operation and universal set have the same symbol

If A,B and C are finite sets. U is the finite universal set, then

(i) n(A U B) = n(A) +n(B) – n(A∩B)

(ii) n(A U B) = n(A) +n(B) A, B are disjoint non-void sets.

(iii) n(A-B) = n(A) –n(A∩B)

(iv) n(A ΔB) = Number of elements which belong to exactly one of A or B

= n((A-B) U (B-A))

(v) n(A U B U C) = n(A) + n(B) + n(C) – n(A∩B) – n(B∩C) – n(A∩C)+n(A∩B∩C)

(vi) No. Of elements in exactly two of the sets A,B,C

= n(A∩B) + n(B∩C)+n(C∩A)-3n(A∩B∩C)

(vii) No. Of elements in exactly one of the sets A,B,C

= n(A) +n(B)+n(C)-2n(A∩B)-2n(B∩C)-2n(A∩C)+3n(A∩B∩C)

(viii) n(A’ U B’) = n((A∩B)’) = n(U) – n(A∩B)

(ix) n(A’∩B’) = n((AUB)’) = n(U)-n(A∩B)

Laws of algebra of sets

1. Idempotent laws

A U B = A

A∩A = A

2. Identity laws

3. Commutative laws

4. Associative laws

5. Distributive laws

6. De-Morgan's laws

## No comments:

Post a Comment