Relations and Functions

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New answer posted

4 months ago

0 Follower 34 Views

V
Vishal Baghel

Contributor-Level 10

(i) f:NN given by f(x)=x2

For, x1,x2N , f(x1)=f(x2)

x12=x22

x1=x2N

So, f is one-one/ injective

For xN , i.e., x=1,2,3....

Range of f(x)={12,22,32...}={1,4,9...}N

i.e., co-domain of N

So, f is not onto/ subjective

(ii) f:ZZ given by f(x)=x2

For, x1,x2Z , f(x1)=f(x2)

x12=x22

x1=±x2Z

i.e., x1=x2 and x1=x2

So, f is not one-one/ injective

For xZ , x=0,±1,±2,±3....

Range of f(x)={02,(±1)2,(±2)2,(±3)2...}

{0,1,4,9....} co-domain Z

So, f is not onto/ subjective

(iii) f:RR given by f(x)=x2

For, x1,x2R , f(x1)=f(x2)

x12=x22

x1=±x2

So, f is not injective

For xR

Range of f(x)={x2,xR} gives a set of all positive real numbers

Hence, range of f(x) co-domain of R

So, f is not subjective

(iv) f:NN given by&n

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New answer posted

4 months ago

0 Follower 3 Views

V
Vishal Baghel

Contributor-Level 10

The fx n is f(x)=1x , which is a f:R*  R* and R* is set of all non-zero real numbers

For, x1,x2R*,f(x1)=f(x2)

1x1=1x2

x1=x2 So, f is one-one

For, yR*, x=1f(x)=1y such that

So, f(x)=y

So, every element in the co-domain has a pre-image in f

So, f is onto

If f:NR* such that f(x)=1x

For, x1,x2N, f(x1)=f(x2)

1x1=1x2

x1=x2 So, f is one-one

For, yR* and f(x)=y we have x=1yN

Eg., 3R* so x=13N

So, f is not onto

New answer posted

4 months ago

0 Follower 3 Views

V
Vishal Baghel

Contributor-Level 10

The given relation in set N defined by

R= { (a, b):a=b2, b>6}

For (2,4),        4>6 is not true

For (3,8),     8>6  but  3= 8-2 ⇒3=6 is not true

For (6,8),      8>6 and 6= 8-2 ⇒6=6 is true

And for (8,7), 7>6 but 8= 7-2 ⇒8=5 is not true

Hence, option (C) is correct

New answer posted

4 months ago

0 Follower 18 Views

V
Vishal Baghel

Contributor-Level 10

The set in A={1,2,3,4}

The relation in this set A is given by

R={(1,2),(2,2),(1,1),(4,4),(1,3),(3,3),(3,2)}

R is reflexive as (1,1),(2,2),(3,3),(4,4)R

As, (1,2)R but (2,1)R

R is not symmetric

For (1,2)R and (2,2)R;(1,2)R

And for (1,3)R and (3,2)R;(1,3)R

∴ R is transitive

Hence, option (B) is correct

New answer posted

4 months ago

0 Follower 25 Views

V
Vishal Baghel

Contributor-Level 10

The given relation in the set L= all lines in XY plane is defined as

R={(L1,L2):L1 is parallel to L2}

Let L1A then as L1 is parallel to L1 ,

(L1,L1)R

So, R is reflexive

Let L1,L2A and (L1,L1)R

Then, L1 is parallel to L2

L2 is parallel to L1

So, (L2,L1)R

i.e., R is symmetric

Let L1,L2,L3A and (L1,L2) and (L2,L3)R

Then, L1?L2 and L2?L3

So, L1?L3

i.e., (L1,L2)R

So, R is transitive

Hence, R is an equivalence relation

The set of lines related to y=2x+4 is given by the equation y=2x+C where C is some constant.

New answer posted

4 months ago

0 Follower 37 Views

V
Vishal Baghel

Contributor-Level 10

The given relation in set A of all polygons is defined as

R= {(P1,P2):P1 and P2 have same number of sides }

Let P1A ,

As number of sides (P1) = number of sides (P1)

(P1,P1)R

So, R is reflexive.

Let P1,P2A and (P1,P2)R

Then, number of sides of P1 = number of sides of P2

Number of sides of P2 = number of sides of P1

i.e., (P2,P1)R

so, R is symmetric.

Let P1,P2,P3A and (P1,P2) and (P2,P3)R

Then, number of sides (P1) = number of sides (P2)

Number of sides (P2) = number of sides (P3)

So, number of sides (P1) = number of sides (P3)

I.e., (P1,P3)R

So, R is transitive.

Hence, R is an equivalence relation.

...more

New answer posted

4 months ago

0 Follower 13 Views

V
Vishal Baghel

Contributor-Level 10

The given relation to set A of all triangles is defined as

R= {(T1,T2):T1 is similar to T2}

For T1A ,

T1 is always similar to T1

So, (T1,T1)R . Hence R is reflexive.

For T1,T2A and (T1,T2)R we have

T1T2(similar)

T2T1 i.e., (T2,T1)R

so, R is symmetric.

for, T1,T2,T3A and (T1,T2)R and (T2,T3)R

T1T2 and T2T3

i.e., T1T3 (T1,T3)R

so, R is transitive

 R is an equivalence relation.

Given, sides of T1 are 3,4,5

Sides of T2 are 5,12,13

Sides of T3 are 6,8,10

As 35412513 we conclude that T1 is not similar to T2

As 561281310 we conclude that T2 is not similar to T3

But as 36=48=510=12 we conclude that 

...more

New answer posted

4 months ago

0 Follower 26 Views

V
Vishal Baghel

Contributor-Level 10

The given relation in set A of points in a plane is

R=  { (P, Q): distance of point P from origin=distance of point Q from origin}

If O is the point of origin

R=  { (P, Q):PO=QO}

Then, for PA we have PO=PO

So,   (P, P)R

i.e., P is reflexive

for,  P, QA and  (P, Q)R we have

PO=QO

QO=PO i.e.,   (Q, P)R

i.e., R is symmetric

for P, Q, SA and  (P, Q)& (Q, S)R

PO=QO and QO=SO

PO=SO

i.e.,   (P, S)R

so, R is transitive

Hence, R is an equivalence relation

For a point P (o, o) the set of all points related to P i.e., distance from origin to the points are equal is a circle with center at origin (o, o) by the definition of circle

New answer posted

4 months ago

0 Follower 19 Views

V
Vishal Baghel

Contributor-Level 10

Let A= {a,b,c}

(i) R= {(a,b),(b,a)} is a relation in set A

So, (a,b)R and (b,a)R Symmetric

(a,a)R not reflexive

(a,b)R,(b,a)R but (a,a)R  not transitive

(ii) R= {(a,b),(b,c),(a,c)} is a relation in set A

So, (a,a)R not reflexive

(a,b)R but (b,a)R not symmetric

(a,b)R&(b,c)R and also (a,c)R transitive

(iii) R= {(a,a),(b,b),(c,c),(a,b),(b,a),(a,c),(c,a)}

So, (a,a),(b,b),(c,c)R Reflexive

(a,b)R(b,a)R Symmetric

(a,c)R(c,a)R

(b,a)R and (a,c)R

But (b,c)R not transitive

(iv) R= {(a,a),(b,b),(c,c),(a,b),(b,c),(a,c)} is s relation in set A

So, (a,a),(b,b),(c,c)R reflexive

(a,b)&(b,c)R so, (a,c)R transitive

(a,b)R but (b,a)R not symmetric

(v) R= {(a,a),(a,b),(b,a)}

So, (b,b)R not reflexive

(a,b)R and (b,a)R symmetric

And (a,b)R&(b,a)R

and also (a,a)R transitive

New answer posted

4 months ago

0 Follower 13 Views

V
Vishal Baghel

Contributor-Level 10

We have,

A= {x2,0x12}

The relation in set A is defined by

R= { (a,b):|ab| is a multiple of 4}

For all aA ,

|aa|=0 is a multiple of 4

So, (a,a)R i.e., R is reflexive

For a,bA&(a,b)R we have,

|ab| is multiple of 4

|(ba)| is multiple of 4

|ba| is multiple of 4

So, (b,a)R

i.e., R is symmetric

for a,b,cA &(a,b)R&(b,c)R

|ab| & |bc| is a multiple of 4

So |ab|+|bc| is also a multiple of 4

|ab+bc| is a multiple of 4

|ac| is a multiple of 4

So, (a,c)R

i.e., R is transitive

Hence, R is an equivalence relation.

Finding all set of elements related to 1

For aA

Then, (a,1)R i.e., |a1| is a multiple of 4

So, a can be 0 ≤ a ≤ 12

Only,

|11|=0

|51|=4 is a multiple of 4

...more

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