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RD Sharma Class 12 Exercise 3.8 Inverse Trigonometry functions Solutions Maths - Download PDF Free Online

RD Sharma Class 12 Exercise 3.8 Inverse Trigonometry functions Solutions Maths - Download PDF Free Online

Updated on Jan 21, 2022 12:33 PM IST

The CBSE Board students widely use the RD Sharma Solution books to clear their doubts in their homework and score good marks in their public examinations. However, every student cannot depend on a tutor to help them clear their doubts 24 x 7. Significantly, the students who find it difficult to cope with the Inverse Trigonometry portions can use the RD Sharma Class 12th exercise 3.8 books.

RD Sharma Class 12 Solutions Chapter3 Inverse Trigonometric Functions-Other Exercise

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Inverse Trigonometric Functions Excercise:3.8

Inverse trigromtery functions exercise 3.8 question 1 (I)

Hint:
As we know that the value of sin(sin1x) is x for x[1,1]
Given:
We have,
sin(sin1725)
Solution:
So here in the expression already present the form of sin(sin1x)
sin(sin1725)=725

Inverse trigromtery functions exercise 3.8 question 1 (II)

Answer:

1213
Hint:
As we know that the value of sin(sin1x) is x for x[1,1]
Given:
We have,
sin(cos1513)
Solution:
Here in the place of sin1x there is cos1x.
So we convert cos1x into sin1x.
Let’s suppose that
cos1513=αcosα=513sin(cos1513)=sinα
Let, inΔABC, angle CAB=α and right angle at B
cosα=513=BH

(AC)2=(AB)2+(BC)2(13)2=52+(BC)2(BC)2=16925
BC=±12 [we will ignore the -ve sign because BC is a length and it can’t be -ve.]
BC=12
sin=1213
So, we required α and that is 1213
sin(cos1513)=sinα=1213

Inverse trigromtery functions exercise 3.8 question 1 (III)

Answer:

2425
Hint:
As we know that the value of (sin1x) is x for x[1,1]
Given:
We have sin(tan1(247))
Solution:
Here in the place of sin1xwe have tan1x.
So, we convert tan1x to sin1x.
Let’s suppose that,
tan1(247)=αtanα=247
Let, in ΔABC, angle CAB=α and right angle at B.

tanα=PB=247(AC)2=(AB)2+(BC)2=72+(24)2=49+576=625
=+25 [we will ignore the -ve sign because AC is a length and it can’t be -ve.]
AC=25
sinα=2425sin(tan1(247))=sinα=2425 [since, tan1(247)=α]

Inverse trigonometric functions exercise 3.8 question 1 (iv)

Answer:

1517

Hint:
As we know that the value of (sin1x) is x for x[1,1]
Given:
We have
sin(sec1(178))
Solution:
So here in place of sin1x there is sec1x.
So, we convert sec1x into sin1x
Let’s we suppose that,
sec1178=αsecα=178
Let, in ΔABC, angle CAB=α and right angle at B.

secα=HB=178(AC)2=(AB)2+(BC)2(17)2=82+(BC)2(BC)2=28964
BC=±15 [we will ignore the -ve sign because BC is a length and it can’t be -ve]
BC=15
sinα=PH=1517sin(sec1(178))=1517

Inverse trigonometric functions exercise 3.8 question 1 (v)

Answer:

54
Hint:
As we know that the value of cosec(cosec1x) is x for x(,1)(1,)
Given:
We have
cosec(cos135)
Solution:
In place of cosec1x here is cos1x
So, we convert cos1x into cosec1x.
Let’s suppose that,
cos135=αcosα=35=BH
Let, in ΔABC, angle CAB=α and right angle at B.

(AC)2=(AB)2+(BC)252=32+(BC)2259=(BC)2
BC=±4 [we will ignore the -ve sign because BC is a length and it can’t be -ve]
BC=4
cosecα=HP=54cosec(cos135)=54

Inverse trigonometric functions exercise 3.8 question 1 (vi)

Answer:

135

Hint:
As we know that the range of sec(sec1x) is x for x(,1)(1,)
Given:
We have
sec(sin1(1213))
Solution:
In place of sec1x there is sin1x
So, we convert sin1x into sec1x .
Let’s suppose that,

sin11213=αsinα=1213
Let, in ΔABC, angle CAB=α and right angle at B.

(AC)2=(AB)2+(BC)2(13)2=(AB)2+(12)2(AB)2=25
AB=±5 [we will ignore the -ve sign because AB is a length and it can’t be -ve]
AB=5
secα=135sec(sin1(1213))=secα=135sec(sin1(1213))=135

Inverse Trigonometric functions exercise 3.8 question 1 (vii)

Answer:

158

Hint:
As we know that the value of tan(tan1x) is x for xR ( real number) 
Given:
We have
tan(cos1(817))
Solution:
In place of tan1x here is cos1x
So, we convert cos1x into tan1x.
Let’s suppose that,
cos1(817)=αcosα=817=BH
Let, in ΔABC, angle CAB=α and right angle at B.


(AC)2=(AB)2+(BC)2(17)2=82+(BC)2(BC)2=28964(BC)2=25
BC=±15 [we will ignore the -ve sign because BC is a length and it can’t be -ve]
BC=15
tan(cos1(817))=tanαtanα=158tan(cos1(817))=158

Inverse Trigonometric functions exercise 3.8 question 1 (viii)

Answer:

34

Hint:
As we know that the range of cot(cot1x) is x for xR ( real number) 
Given:
cot(cos1(35))
Solution:
In place of cot1x here is cos1x
So, we convert cos1x into cot1x.
Let’s suppose that,
cos1(35)=αcosα=35=BH
Let, in ΔABC, angle CAB=α and right angle at B.

(AC)2=(AB)2+(BC)2(5)2=32+(BC)225=9+(BC)2(BC)2=16
BC=±4 [we will ignore the -ve sign because BC is a length and it can’t be -ve]
BC=4cot(cos1(35))=cotccotα=34cot(cos1(35))=34


Inverse Trigonometric functions exercise 3.8 question 1 (ix)

Answer:

725
Hint:
As we know that the range of (cos1x) is x for x[1,1]
Given:
We have
cos(tan1(247))
Solution:
In place of cos1x here is tan1x
So, we convert tan1x into cos1x .
Let’s suppose that,
tan1(247)=αtanα=247
Let, in ΔABC, angle CAB=α and right angle at B.

(AC)2=(AB)2+(BC)2(AC)2=72+(24)2(AC)2=625
AC=±25 [we will ignore the -ve sign because AB is a length and it can’t be -ve]
AC=25
cos(tan1(247))=cosαcosα=725cos(tan1(247))=725

Inverse Trigonometric functions exercise 3.8 question 2 (i)

Hint:
We convert in the form of tan(α+β) so we know the formula of it.
Given:
We have to prove that tan(cos145+tan123)=176
Solution:
LHS= tan(cos145+tan123)
Let suppose that cos145=α and tan123=β,
cosα=45 and tanβ=23tan(α+β)=tanα+tanβ1tanαtanβ
But we have not tanα. We have only tanβ. So, we convert cosα into tanα.
cosα=45=BH
Let, in ΔABC, angle CAB=α and right angle at B.


(AC)2=(AB)2+(BC)2(5)2=42+(BC)2(BC)2=2516
BC=±9
BC=3
tanα=34

[tanα=34andtanβ=23]
tan(α+β)=tanα+tanβ1tanαtanβ=34+23134×23=9+812612=176=RHStan(cos145+tan123)=176 [ we take LCM of 3,4]
Hence proved.

Inverse trigonometric functions exercise 3.8 question 2 (ii)

Hint:
We convert in the form of cos(α+β)and we know the formula of it.
Given:
We have to prove cos(sin135+cot132)=6513
Solution:
LHS = cos(sin135+cot132)
Let’s suppose that sin135=αand cot132=β.
sinα=35andcotβ=32
cos(α+β)=cosαcosβsinαsinβ
Here, we only have sinα and cosβ.So we have to find cosαand sinβ.
sinα=35=BH
Let, in ΔABC, angle CAB=α and right angle at B.

(AC)2=(AB)2+(BC)2(5)2=(AB)2+32(AB)2=259
AB=±4
cosα=45
Let, in ΔPQR, angle RPQ=β and right angle at B.
cotβ=32=BP

(PR)2=(QR)2+(PQ)2(PR)2=22+32(PR)2=4+9
PR=±13 [we will ignore the -ve sign because PR is a length and it can’t be -ve]
PR=13
PR=13sinβ=213,cosβ=313cos(α+β)=cosαcosβsinαsinβ=45×313213×35=125136513cos(α+β)=6513=RHS

Inverse trigonometric functions exercise 3.8 question 2 (iii)

Hint:
We convert expression in the form of tan(α+β) so we know the formula of it.
Given:
We have to prove tan(sin1513+cos135)=6316
Solution:
LHS = tan(sin1513+cos135)
sin1513=αandcos135=β
sinα=513andcosβ=35
tan(α+β)=tanα+tanβ1tanαtanβ …(i)
But we have not tanα and tanβ. So, we find out first then we put in equation (i)
sinα=513=PH
Let, in ΔABC, angle CAB=α and right angle at B.

(AC)2=(AB)2+(BC)2(13)2=AB2+52(AB)2=144
AB=±12 [we will ignore the -ve sign because AB is a length and it can’t be -ve]
AB=12
tanα=512

Let, in ΔPQR, angle RPQ=β and right angle at B.
cotβ=35=BP

(PR)2=(QR)2+(PQ)2(5)2=32+(QR)2(QR)2=16
QR=±4
QR=4
tanβ=43
Now, tan(α+β)=tanα+tanβ1tanαtanβ=512+431512×43 [ put, tanα=512 and tanβ=43]
[ we take LCM of 3 and 12]
=5+1612362036=21121636=2112×3616=211×316tan(α+β)=6316=RHS
Hence proved.

Inverse trigonometric functions exercise 3.8 question 2 (iv)

Answer:

Hint:
We convert in the form of sin(α+β)and we know the formula of it.
Given:
We have to prove sin(cos135+sin1513)=6365
Solution:
LHS = sin(cos135+sin1513)
Let’s suppose that cos135=αandsin1513=β
cosα=35andsinβ513 and
sin(cos135+sin1513)sin(α+β)=sinαcosβ+cosαsinβ
…(i)
Here we don’t have sinα.cosβ. So, we find out it and then put all the values in equation (i)
Let, in ΔABC, angle CAB=α and right angle at B.
cosα=35=BH

(AC)2=(AB)2+(BC)2(5)2=(3)2+(BC)2252=92+(BC)2(BC)2=16
BC=±4
BC=4
sinα=45
Let, in ΔPQR, angle RPQ=β and right angle at B.
sinβ=513=PH

(PR)2=(PQ)2+(QR)2(13)2=(PQ)2+52169=(PQ)2+25(PQ)2=144
PQ=±12 [we will ignore the -ve sign because PQ is a length and it can’t be -ve]
PQ=12
cosβ=1213
Now, sin(α+β)=sinαcosβ+cosαsinβ=45×1213+35×513=4865+1565sin(α+β)=6365=RHS
Hence proved.

Inverse trigromtery functions exercise 3.8 question 3 (i)

Answer:

x=±3536
Hint:
We know the value ofcos(cos1x) is x for x[1,1]
Given:
We have to solve cos(sin1x)=16 to find the value of x.
Solution:
Here, we have given sin1x in place of cos1x. So, we convert sin1x into cos1x
Let’s suppose that,
sin1x=α
sinα=x
We use the identity,
sin2α+cos2α=1x2+cos2α=1cos2α=1x2
cosα=±1x2 [But we can eliminate negative value of cosα , because in RHS of the question only positive value is given.]
cosα=1x2 …(i)
Now,
cos(sin1x)=16cosα=16 .....(ii)

From equation (i) and (ii) we get,
1x2=16
Squaring on both sides,
(1x2)2=(16)21x2=136x2=1136x2=3536x=±3536
Therefore, the answer is x=±3536 .

Inverse trigromtery functions exercise 3.8 question 3 (ii)

Answer:

x=±12
Hint:
As we know that the value ofcos(cos1x) is x for x[1,1]
Given:
We have to solve cos(2sin1(x))=0 to find the value of x.
Solution:
So, we convert 2sin1(x) into cos1(x)
cos(2sin1(x))=cos(2sin1x) [sin1(x)=sinx]
=cos(2sin1x) …(i) [ as, cos is even function, so cos(x)=cosx]
Let’s suppose,

sin1x=α …(ii)
sinα=x …(iii)


Given,
cos(2sin1(x))=0
cos(2sin1(x))=0 … [ from eqn(i) ]
cos2α=0 …[ using (ii) ]
12sin2α=0 [cos2α=12sin2α ]
12x2=02x2=1x2=12x=±12

Therefore, the answer is x=±12

The 3rd chapter in mathematics, Inverse Trigonometry for Class 12, is not easy for many students to understand. Especially in the eighth exercise, which is Exercise 3.8, the students must solve the functions as learned from the previous exercises. The concepts given here are regarding solving sine, cosine, tangent, cotangent, secant, and cosecant functions. There are about fifteen questions, including the subparts in this exercise 3.8. If they find it hard, the RD Sharma Class 12 Chapter 3 Exercise 3.8 solutions will lend them a helping hand.

The solutions in this book are created by experts and verified according to the updated syllabus. You can use this guide to complete your homework and make your assignments too. As it follows the NCERT pattern, it is beneficial for the students who pursue their education at CBSE institutions. If you see yourself scoring low marks in the chapter Inverse Trigonometry, use the solutions given in the Class 12 RD Sharma Chapter 3 Exercise 3.8 Solution and understand the concepts. The different ways to solve a single question are given in the material. Soon, you will find yourself crossing your benchmark score.

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Chapter-wise RD Sharma Class 12 Solutions

Frequently Asked Questions (FAQs)

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The RD Sharma books are a set of solutions provided by experts in the educational sector. Hence, the students can use it to prepare for their exams.

2. What to do if I have any doubts about the Inverse Trigonometry chapter?

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With the solutions of educational experts, RD Sharma Class 12th exercise 3.8 solution consists of many methods of solving a mathematical function. Hence, both the toppers and the average students can find it easier to choose the way they understand and go ahead with it.  

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