Let A={1,2,3}, B={3,4} & C={4,5,6}. Find
(i) A$\times$(B∩C) (ii) (A$\times$B)∩(A$\times$C) (iii) A$\times$(B∪C) (iv) (A$\times$B)∪(A$\times$C)
(i) A={1,2,3}, B∩C={4}
A$\times$(B∩C)={(1,4),(2,4),(3,4)}
(ii) A$\times$B={(1,3),(1,4),(2,3),(2,4),(3,3),(3,4)}
A$\times$C={(1,4),(1,5),(1,6),(2,4),(2,5),(2,6),(3,4),(3,5),(3,6)}.
(A$\times$B)∩(A$\times$C) = {(1,4),(2,4),(3,4)}
A$\times$(B∩C) = (A$\times$B)∩(A$\times$C)
(iii) B={3,4}, C={4,5,6}
∴ B∪C = {3,4,5,6}
A$\times$(B∪C) = {(1,3),(1,4),(1,5),(1,6),(2,3)(2,4),(2,5),(2,6),(3,3)(3,4),(3,5),(3,6)}.
A$\times$B & A$\times$C were calculated earlier.
(A$\times$B)∪(A$\times$C) ={(1,3),(1,4),(2,3)(2,4),(3,3)(3,4),(1,5),(1,6),(2,5),(2,6),(3,5),(3,6)}
A$\times$(B∪C) = (A$\times$B)∪(A$\times$C).
Let P={a,b,c}. Find the set P$\times$P$\times$P.
P$\times$P$\times$P = {(a,a,a),(a,a,b),(a,a,c),(a,b,a),(a,b,b),(a,b,c),(a,c,a),(a,c,b),(a,c,c),(b,a,a),(b,a,b),(b,a,c),(b,b,a),(b,b,b),(b,b,c),(b,c,a),(b,c,b),(b,c,c),(c,a,a),(c,a,b),(c,a,c),(c,b,a),(c,b,b),(c,b,c),(c,c,a),(c,c,b),(c,c,c)}.
(P$\times$P$\times$P) = 27.
1.) {($x,y$) | $x$ and $y$ are real numbers & $x^2+y^2=1$}⊆$\R^2$
This is not a cartesian product of two sets.
2.) A={Ramu,Babu,Ramesh,Kumar,Siva}.
B={Laxmi,Manju,Mani}.
R={(Ramesh,Mani),(Ramu,Manju),(Babu,Laxmi)}.
Ramesh & Mani - are married Ramu & Manju - are married Babu & Laxmi - are married
${\bold{\text{Definition:}}}$
Let A and B be any two nonempty sets. A relation R from A to B is a nonempty subset of A$\times$B.
#(A $\times$ B) = #(A).#(B)
How many relations are possible between A & B? How many subset of A$\times$B are possible?
If A is any nonempty set, then the number of possible subset of A is 2#(A).
∴ The no. of possible nonempty subsets of A$\times$B is 2#(A$\times$B)$-$1
Let A={1,2,3}
$\quad$ B={2,3,4}
Notice that A$\times$B is itself a relation between A and B. This relation is called the universal relation.
For any two sets A & B, A$\times$B is called the universal relation.
A={1,2,3}
B={2,3,4}
R={(1,2),(1,3),(2,2),(2,3),(3,4)}.
A={Ramu, Babu, Ramesh, Kumar, Siva}
B={Laxmi, Manju, Mani}
R={(Ramesh,Mani),(Ramu,Manju),(Babu,Laxmi)}
A={1,2,3,4,5}
B={-1,0,4,9,25}
R={(x,y) ∈ A × B | y=x2}.
R={(2,4),(3,9),(5,25)}
Let A and B be two nonempty sets and let R be a relation between A and B.
The domain(R) is the set of all first elements from the ordered pairs in R.
The set B is called as the codomain of R.
The set of all second elements from the ordered pairs in R is called the range of R.
Let A = {1,2,3,4,5,6}
R = {(x,y)∈A × A | y=x+1}.
R={(1,2),(2,3),(3,4),(4,5),(5,6)}
Domain(R) = {1,2,3,4,5}
Codomain(R) = {1,2,3,4,5,6}
Range(R) = {2,3,4,5,6}.
A={4,9,10,25}
B={-5,-3,-2,1,2,3,5}
R={(x,y)∈A × B | x is the square of y}.
R={(4,-2),(4,2),(9,-3),(9,3),(25,-5),(25,5)}.
Domain(R) = {4,9,25}
Codomain(R) = {-5,-3,-2,1,2,3,5}
Range(R) = {-3,-2,-5,2,3,5}.
#(A)=4 $\quad \quad$ #(B)=7
#(A × B)=4 × 7=28.
∴ The no. of possible relations from A to B is 228-1.
Consider the set of all natural numbers.Define R={(n,m)∈ $\N$ × $\N$ | m=n+5}.
$\N $ - set of all natural numbers.
R is an infinite set.
R = {(n,n+5) | n is a natural number}.
R’= {(n,m)∈ $\N$ × $\N$ | m=n+5 & n≤4}.
= {(1,6),(2,7),(3,8),(4,9)}.
Let
A ={1,2,3,5}
B ={4,6,9}
R={(x, y) $\in$ A × B $\mid$ the difference between x & y is an odd number }.
= {(1,4),(1,6),(2,9),(3,4),(3,6),(5,4),(5,6)}.
A={1,2,3,5}
R={(x,y)∈ A × A | the difference between x and y is an odd number}.
={(1,2),(2,1),(2,3),(2,5),(3,2),(5,2)}
Whenever (x,y)∈R $\rightarrow$ (y,x)∈R.
Definition: Let A be a nonempty set and let R be a relation on A ,i.e., R is a nonempty subset of AxA. We say that R is a Symmetric.
if (x,y)∈R $\implies$ (y,x)∈R.