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RD Sharma Class 12 Exercise 2.3 Function Solutions Maths - Download PDF Free Online

RD Sharma Class 12 Exercise 2.3 Function Solutions Maths - Download PDF Free Online

Edited By Kuldeep Maurya | Updated on Jan 20, 2022 10:43 AM IST

RD Sharma books are no less than a Math bible for students as they contain concepts and chapters that help students understand the subject. Similarly, RD Sharma Class 12th Exercise 2.3 is specifically designed for Class 12 students to prepare for their exams. Therefore, students will find this material very helpful for their preparation as they are preparing for their Class 12 exams and the entrance exams that will be conducted in the future.

RD Sharma Class 12 Solutions Chapter 2 Functions - Other Exercise

Functions Excercise: 2.3

Functions Exercise 2.3 Question 1 (i).

Answer :fog(x)=xandgof(x)=x
Hint : If f:AB and g:BC be two given functions then the composite of f and g denoted by gof
(gf):AC(gf)(x)=g{f(x)}xA
And dom (gof)= dom f
Given : Here given that f(x)=exandg(x)=logex
Here we have find out fog and gof
Solution :
Here first we will find out fog
Here we have,
f(x)=ex and g(x)=logexfg(x)=f{g(x)}=f{logex}=loge(ex)=xfg(x)=x
Now, we find out gof, we have ,
f(x)=ex&g(x)=logexgf(x)=g{f(x)}=g{ex}=loge(ex)=xgf=x

Functions Exercise 2.3 Question 1 (ii).

Answer :
gf(x)=cosx2fg(x)=cos2x
Hint : Domain of f and domain g = R
Range of f=(0,)
Range of g g=(1,1)
Range of f domain of g
gof exists
and Range of g domain of f
fog exists
Given : Here given that
f(x)=x2andg(x)=cosx
Solution :
Here first we will find out gof,
We have,
f(x)=x2 and g(x)=cosxgf(x)=g{f(x)}=g{x2}=cosx2
and again for fog
fog(x)=f{g(x)}=f{cosx}=cos2x
NOTE :fog is defined only when range (g)dom(f)and domfog=dom(g).

Functions Exercise 2.3 Question 1 (iii).

Answer :
fg(x)=|sinx|gf(x)=sin|x|
Hint : The Range of f=(0,)f=(0,) domain g(R)
gof exists
And Range of g=[1,1] domain R
fog exists
Given : Here given that
f(x)=|x|andg(x)=sinx
Here we have to find out fog and gof
Solution :
First , we will find out fog(x)
fg(x)=f{g(x)}=f{sinx}=|sinx|
Again, we find out gof(x)
gf(x)=g{f(x)}=g{|x|}=sin|x|

Functions Exercise 2.3 Question 1 (iv).

Answer :
gf(x)=ex+1fg(x)=ex+1
Hint : The Range of f=RDomain of f=R
fog exists
Given : Here given that
f(x)=x+1 and g(x)=ex
Here we have to find out gf(x)andfg(x)
Solution :
First, we will find out gof(x)
We have,
gf(x)=g{f(x)}=g{(x+1)}=ex+1
And again, we will find out fog(x)
fg(x)=f{g(x)}=f{ex}=ex+1 So, gf(x)=ex+1 and fg(x)=ex+1

Functions Exercise 2.3 Question 1 (v).

Answer :
fg(x)=sin1(x2)gf(x)=(sin1x)2
Hint :
Domain(fg)={x:xdomain of g andg(x)domain of f}Domain of(fg)={x:xRandx2[1,1]}Domain offg=[1,1]
Given : Here given that
f(x)=sin1xandg(x)=x2
Here, we have to compute fog(x)andgof(x)
Solution :
Here we have to compute fog :
fg:[1,1]Rfg=f{g(x)}=f{x2}=sin1(x2)
Now, we have to find out gof:
Clearly, the range of f is subset of the domain of g.
ff:[1,1]Rgf(x)=g{f(x)}=g{sin1x}=(sin1x)2

Functions Exercise 2.3 Question 1 (vi).

Answer :
gf(x)=sin(x+1)fg(x)=sinx+1
Hint :f:RR;g:R[1,1]
Given : Here given that
f(x)=x+1andg(x)=sinx
we have to compute fog(x) and gof(x)
Solution :
First, we have to compute fog
Clearly, the range of g is a subset of the domain f.
Set of the domain of f.
fog:RR
fog(x)=f{g(x)}
=f(sinx)
=sin(x+1)
Now, we will compute gof
gof(n)=g{f(n)}
=g{x+1}
=sin(x+1)

Functions Exercise 2.3 Question 1 (vii).

Answer :
fg(x)=2x+4gf(x)=2x+5
Hint : Domain fg={x:xR and 2x+3R}
Now, we have to compute fog and gof
Given : Here given that
f(x)=x+1 and g(x)=2x+3
Solution :
First, we will compute fog
Here, f:RR,g:RR
Clearly the range of g is a subset of the domain of f.
fg:RRfg(x)=f{g(x)}=f(2x+3)=2x+3+1=2x+4
Now, we will compute gof
Clearly the range of f is subset of the domain of g
fg:RRgf(x)=g{f(x)}=g(x+1)=2(x+1)+3=2x+5.
Hence, fg(x)=2x+4 and gf(x)=2x+5

Functions Exercise 2.3 Question 1 (viii).

Answer :
fg(x)=Cgf(x)=sinC2
Hint : The range of g is a subset of the domain of f .
Given: Here given that
f(x)=C and g(x)=sinx2
Here we have to compute fogand gof.
Solution :
First , we will compute the fog
We have, fg:RR
fg(x)=f{g(x)}=f(sinx2)=C
Now we will compute gof
Clearly the range of f is a subset of the domain of g .
fg:RRgf(x)=g{f(x)}=g(C)=sinC2

Functions Exercise 2.3 Question 1 (ix).

Answer :
fg(x)=3x24x+2(1x)2gf(x)=(x2+2)(x2+1)
Hint :f:R[2,]
Given : Here given that f(x)=x2+1 and g(x)=111x
For domain of g=1x0
x1.
Domain of g=R{1}
g(x)=11x=1x11x=x1x
For range of g
y=x1xyxy=xy=xyxy=x(y1)x=yy1
Range of g=R{1}
g:R{1}R{1}
Solution :
First, we compute fog
Here clearly the range of g is subset of domain of f.
fg:R{1}Rfg(x)=f(g(x))f(x1x)=(x(1x))2+2=x2+2x2+24x(1x)2fg(x)=3x24x+2(1x)2
Now, we will compute gof

Clearly the range of f is a subset of the domain of g

gf:RRgf(x)=g(f(x))=g(x2+2)=111(x2+2)=11(x2+2)=x2+2x2+1gf(x)=x2+2x2+1

Functions Exercise 2.3 Question 2.

Given : Here given that
f(x)=x2+x+1 and g(x)=sinx
To prove : We have to prove that fggf
Solution :
First, we have to compute fog and gof
For fog
fg(x)=f(g(x))=f(sinx)=sin2x+sinx+1 ...(i)
And now for gof
gf(x)=g(f(x))=g(x2+x+1)=sin(x2+x+1) ... (ii)
From enq. (1) and (2) we proved that
fggf

Functions Exercise 2.3 Question 3.

Given : Here given that f(x)=|x|
To prove : Here we have to prove that
fof=f
Solution :
Here we have to compute
fof(x)
We have ,
(ff)(x)=f(f(x))=f(|x|)=||x||=|x|=f(x)
So, (ff)(x)=f(x)xR
Hence, fof=f

Functions Exercise 2.3 Question 4 (i).

Answer :fg(x)=2x2+7
Given : Here given that
f(x)=2x+5 and g(x)=x2+1
Here we have to compute fog
Solution :
Since f(x) and g(x) are polynomials.
f:RR and g:RRfg(x)=f(g(x))=f(x2+1)=2(x2+1)+5=2x2+2+5=2x2+7
Hence, fog(x)=2x2+7

Functions Exercise 2.3 Question 4 (ii).

Answer : gf(x)=4x2+20x+26
Given : Here given that f(x)=2x+5 and g(x)=x2+1
Here we have to compute gof
Solution :
Since f(x) and g(x) are polynomials.
f:RR and g:RR
gf(x)=g(f(x))=g(2x+5)=(2x+5)2+1=4x2+20x+26
Hence, gf(x)=4x2+20x+26

Functions Exercise 2.3 Question 4 (iii).

Answer :ff(x)=4x+15
Given : Here given that f(x)=2x+5 and g(x)=x2+1
Here we have to compute fof
Solution :
Since f(x) and g(x) are polynomials
f:RR and g:RR
ff(x)=f(f(x))=f(2x+5)=2(2x+5)+5=4x+10+5=4x+15
Hence, ff(x)=4x+15

Functions Exercise 2.3 Question 4 (iv).

Answer :f2(x)=4x2+20x+25
Given : f(x)=2x+5 and g(x)=x2+1
Here we have to find out f2
Hint : If we want to f2 then first we compute f(x)×f(x).
Solution :
Since f(x)=2x5 is a polynomial.
f:RR
f2(x)=f(x)×f(x)=(2x+5)(2x+5)=(2x+5)2f2(x)=4x2+20x+25
In this question we have to prove that
fof=f2
Then first we have to find out fof
For fof
fof(x)=f(f(x))=f(2x+5)=2(2x+5)+5=4x+10+5fof(x)=4x+15 ...(1)
Again we will compute f2
Since
f2(x)=f(x)×f(x)=(2x+5)(2x+5)=4x2+20x+25 ...(2)
From (1) and (2) we have
(fof)(x)=f2(x)
Hence proved

Function Exercise 2.3 Question 5.

Answer : fg(x)=sin2x;gf(x)=2sinx and they are not equal functions.
Given : Here given that f(x)=sinxandg(x)=2x
Here we have to compute gof and fog
Hint : First we will compute gof
we know that f:R[1,1] and g:RR
Clearly the range of f is a subset of the domain of g.
Second, we will compute fog
Clearly the range of g is a subset of the domain of f.
Solution :
gf:RR(gf)(x)=g(f(x))=g(sinx)=2sinx ....(1)
fg:RR So, fg(x)=f(g(x))=f(2x)=sin2x ....(2)
From (1) and (2) clearly foggof
Hence, they are not equal functions.

Function Exercise 2.3 Question 6.

Given : Here given that
f(x)=sinx;g(x)=2x&h(x)=cosx
To prove : Here we have to prove that fg=g(fh).
Solution :
We know that
f:R[1,1] and g:RR
Clearly, the range of g is a subset of the domain of f .
fg:RR
Now,
(fh)(x)=f(x)h(x)=(sinx)(cosx)=12sin(2x)
Domain of h is R.
Since range of sinx is [1,1];1sinsin2x1
12sinsinx212
Range of fh=[12,12]
So, (fh):R[12,12]
Clearly the range of fh is a subset of g
g(fh):RR
Domain of fogandgo(fh) are the same gain
So,
fg(x)=f(g(x))(fg)(x)=f(2x)=sin(2x)
And again ,
g(fh)(x)=g(f(x)h(x))=g(sinxcosx)=2sinxcosx=sin2x
fg(x)=go(fh)(x);xR
Hence, fg=g(fh)

Functions Exercise 2.3 Question 7.

Given : Here given that f is a real function and g is a function given by g(x)=2x.
To prove : Here we have to prove that gf=f+f
Solution : Now, we will take L.H.S. if L.H.S. = R.H.S. then it will be proved.
Take, L.H.S.
gf(x)=g(f(x))=g(f(x))=2(f(x))=f(x)+f(x)= R.H.S. 
Hence, gf=f+f

Functions Exercise 2.3 Question 8.

Answer :
(gof)(x)=loge1x(fg)(x)=loge1x
Hint : Domain of f and g are R
Range of f=(,1)
Range of f=(0,e)
Given : Here given that f(x)=1x and g(x)=logex
Solution :
Clearly Range f domain of g
gf exists
And Range g domain of f
fg
(gf)(x)=g(f(x))=g(1x)=loge1x
Again, we will compute fg
(fg)(x)=f(g(x))=f(logex)(fg)(x)=loge1x

Functions Exercise 2.3 Question 9.

Answer :
(fg)(x)=tan(1x2)(gf)(x)=tan(1x2)
Given : Here given that
f:(π2,π2)R and g:[1,1]R defined as f(x)=tanx and g(x)=1x2
Hint : Since (π2,π2),y(,)
Range of f domain of g=[1,1]
Solution :
First, we compute (fg)(x)
We know that
Let y=f(x)
y=tantanxx=y;x(π2,π2)(fg)(x)=f(g(x))=f(1x2)=tan(1x2)
Again we will compute (gf)(x)
(gf)(x)=g(f(x))=g(tanx)gf(x)=tan(1x2)

Functions Exercise 2.3 Question 10.

Answer :
(fg)(x)=x2+4(gf)(x)=x+4
Given : Here given that
f(x)=x+3 and g(x)=x2+1
Here we have to find out fg and gf
Solution :
First, we will compute fg
(fg)(x)=f(g(x))=f(x2+1)=x2+1+3(fg)(x)=x2+4
Again, we will compute gf
(gf)(x)=g(f(x))=g(x+3)=(x+3)2+1(gf)(x)=x+4
Hence, (fg)(x)=x2+4 and (gf)(x)=x+4

Functions Exercise 2.3 Question 11 (i) .

Answer :(ff)(x)=x22
Hint : Domain f=(2,) and Range (f)=(0,)
Clearly, the range of (f) is not a subset of domain of f.
Given : Here f be a real function given by f(x)=x2
Here we have to compute ff
Solution :
We know that
Domain of (ff)={x:x Domain of f and f(x) Domain (f)}
={x:x(2,) and x2(2,)={x:x(2,) and x22}={x:x(2,) and x24}={x:x(2,)x6=(6,)
Now,
(ff)(x)=f(f(x))=f(x2)=x22ff:(6,)R
Hence, (ff)(x)=x22

Functions Exercise 2.3 Question 11 (ii) .

Answer :(fff)(x)=x222
Hint : Domain (f)=(2,) and range of (f)=(0,)
Given : Here f be a real function given by f(x)=x2
We have to compute fff
Solution :
Clearly the range f is not subset of domain of f.
 Domain (ff)={x:x(2,) and x2(2,)}={x:x(2,) and x22}={x:x(2,) and x24}={x:x(2,) and x26=(6,)
Clearly the range of f=(0,) Domain of (ff)
 Domain of (fff)={x:x(2,) and x2(6,)={x:x(2,) and x26}={x:x(2,) and x236}={x:x(2,) and x38}
Now, we will compute (fff)(x)
First we compute (ff)(x)
(ff)(x)=f(f(x))=f(x2)(ff(x))=x22
Now,
(fff)(x)=(ff)(f(x))=(ff)(x2)
=x222
Hence, (fff)(x)=x222

Functions Exercise 2.3 Question 11 (iii) .

Answer :(fff)(38)=0
Hint : Domain (f)=(2,) and Range (f)=(0,)
Given : Let f be a real function given by f(x)=x2
Now, we will compute (fff)(38)
Solution :
Clearly the range (f) is not a subset of domain of (f)
 Domain of (ff)={x:x Domain of f and f(x) Domain (f)}={x:x(2,) and x2(2,)}={x:x(2,) and x22}={x:x(2,) and x24}={x:x(2,) and x6}=(6,)
Clearly range of f=[0,) Domain of (ff)
Domain of((ff)f)={x:xDomain of f and f(x)Domain(ff)}
 Domain of ((ff)f)={x:x[2,) and x2[,)}
={x:x[2,) and x26}={x:x[2,) and x236}={x:x[2,) and x38}=[38,)
Now, we will compute (fff)(x)
(ff)(x)=f(f(x))=f(x2)=x22
Again we will compute (fff)(x)
(fff)(x)=(ff)(f(x))=(ff)(x2)=(ff)(x2)=x222
Now, (fff)(38)=38222
=3622=622=22=0
Hence, (fff)(38)=0

Functions Exercise 2.3 Question 11 (iv) .

Given : Here given that
f(x)=x2
Now we have to compute f2 and
To prove : We have to prove that fff2
Solution :
First, we will compute f2
f2(x)=f(x)×f(x)=x2×x2=x2
Clearly, Domain (f)=[2,) and Range (f)=[0,]
We observe that the range (f) is not subset of domain of f
 Domain of (ff)={x:x Domain (f) and f(x) Domain (f)}={x:x[2,) and x2[2,)}={x:x[2,) and x24}={x:x[2,) and x6}=[6,)
Now, we will compute (ff)(x)
(ff(x))=f(f(x))=f(x2)=x22
and again for f2
f2(x)=[f(x)]2=[x2]2=x2
Here we see that fff2
Hence, fff2

Functions Exercise 2.3 Question 12 .

Answer :
ff(x)={2+x;0x12x;1<x24x;2<x3
Hint : Range of f=[0,3] domain of f.
Given : Given that f(x)={1+x;0x23x;2x3
Here we have find out fof
Solution :
We have,
Range of f=[0,3] domain of f
ff(x)=f(f(x))=f{1+x;0x23x;2x3ff(x)={2+x;0x12x;1x24x;2x3

Functions Exercise 2.3 Question 13 .

Answer : fg(x)={0,x04x,x<0
gf(x)=0 for all xfg(3)=12,fg(5)=0 and gf(2)=0
Hint : We know about modulus function,
f(x)=|x|+xf(x)={x+x, if x0x+x, if x<0
Given : Let f, g:RR be two function defined as :
f(x)=|x|+xg(x)=|x|x
Here, we have to find out fg(x),gf(x),fg(3),fg(5) and gf(2)
Solution :
Here,
f(x)=|x|+x and g(x)=|x|xf(x)={x+x, if x0x+x, if x<0f(x)={2x, if x00, if x<0g(x)={xx, if x0xx, if x<0g(x)={0, if x02x, if x<0
Thus for x0,gf(x)=g(f(x))
=g(2x)=0
For x<0,gf(x)=g(f(x))
=g(0)=0gf(x)=0xR
Thus for x0,fg(x)=f(g(x))
=f(0)=2(0)=0
For x<0,fg(x)=f(g(x))
=f(2x)=4x
fg(x)={0,x04x,x<0
Again,
f(x)=|x|+x and g(x)=|x|xg(x)=f(g(x))=lg(x)+g(x)=||x|x|+|x|xgf(x)=g(f(x))=|f(x)|f(x)=||x|+x|[|x|+x]
Then,
fg(3)=||3|(3)|+|3|(3)=|3+3|+3+3=6+6=12fg(3)=12
fg(5)=||5|(5)|+|5|(5)=55+55=0fg(5)=0gf(2)=||2|+(2)|[|2|+(2)]=|2+2|[2+2]=44=0gf(2)=0

RD Sharma Class 12th Exercise 2.3 covers many essential topics related to functions and will help students quickly understand many fun and exciting concepts. Here you will learn about different kinds of functions and solve fundamental problems involving them. As this is an important chapter, students can expect many questions from it in entrance exams.

In RD Sharma Class 12th Exercise 2.3, you will learn basic definitions of identity function, modulus function, fractional part function, signum function, etc. Then, you will learn some theories on relations between functions like 'one to one,' 'onto' function, etc., followed by problems. Next, the numerical are divided into different levels to gradually build their problem-solving skills and move on to complex problems.

RD Sharma Class 12th Exercise 2.3 has 20 - Level 1 and 6 - Level 2 example questions that students can use to build their basic problem-solving skills. Level 1 sums contain all the introductory concepts you have covered first in this chapter, followed by Level 2, which has more advanced questions. The Level 2 questions carry more marks but have more complexity, so students have to be perfect in Level 1 sums first.

There are many ways to solve a problem, you don't need to follow the textbook's steps. Students are free to use any method they like to solve a problem as long as it is valid. Getting a thorough knowledge of this material can help students find alternative ways to solve a problem. This saves time and allows students to reduce complexity for their sums.

The following material: RD Sharma Class 12 Solutions Chapter 2 Ex.2.3 is designed by experts to cover all important questions and help students get different alternatives to finding a problem. As these materials are widely used, there might be good chances that their questions can appear in your exams. Therefore, experts suggest that students should practice this material regularly to understand the subject.

RD Sharma Class 12th Exercise 2.3 on Career360 provides the best materials on RD Sharma books free of cost. Never before have these solutions been available so conveniently. Students can take advantage of the informative material and score well in exams. A lot of students have chosen Career360 as the best source for their RD Sharma solutions. People who haven’t yet discovered it should undoubtedly refer to this to score good marks. You can find more expert-created answers to different books on the website, which are free of cost and accessible to everyone.

Chapter-wise RD Sharma Class 12 Solutions

Frequently Asked Questions (FAQs)

1. Can I score good marks in exams by referring to RD Sharma books?

Yes, RD Sharma books are the best material students can refer to for preparation. This material will help them score good marks in exams and get a good hold on the subject. You will easily score good marks if you practice well using this material. RD Sharma Class 12 Chapter 2 Exercise 2.3 is made for students to understand the fundamentals of Functions and prepare well for exams.

2. Do these solutions contain important questions?

Yes, the solutions provided by Career360 contain important questions that are helpful for easy preparation before exams. Students can refer to RD Sharma Class 12 Chapter 2 Exercise 2.3 to get a good idea about the chapter ‘Functions’ and its important questions.

3. What are the advantages of these solutions?

The Class 12 RD Sharma Chapter 2 Exercise 2.3 solution is made by a team of experts who help students prepare well for their exams. Their advantages are:

  • Solutions are easy to understand.

  • Important questions are discussed.

  • Material is updated to the latest version. 

  • Solutions are free of cost.

4. What is a Function?

Elements that are arranged in a group and have certain fixed values are called sets. A function is a set of rules or expressions that define a relationship between two or more sets. You can refer to Class 12 RD Sharma Chapter 2 Exercise 2.3 solution for thorough information on this topic.

5. . What are the different types of Functions?

The different types of functions are: 

  1. One-one function or Injection

  2. Many-one function 

  3. Onto function or Surjection

  4. Bijection

You can learn more about these with examples using RD Sharma Class 12 functions Ex 2.3

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