Q 21 :

Let a≤tan-1x+cot-1x+sin-1x≤b. If α and β denote the minimum and maximum possible values of a and b respectively, then: 

  • α=0, β=π

     

  • α=0, β=π2

     

  • α=π2, β=π

     

  • α=-π2, β=π2

     

(1)

Ans.   α=0, β=π

Explanation:

We know that

   tan-1x+cot-1x=π2

tan-1x+cot-1x+sin-1x=π2+sin-1x

                  -π2≤sin-1x≤π2

⇒-π2+π2≤sin-1x+π2≤π2+π2

⇒0≤π2+sin-1x≤π

⇒0≤tan-1x+cot-1x+sin-1x≤π

∴   α=0,    β=π



Q 22 :

The principal value of  sin-1(-32) is:

  • -2π3

     

  • -π3

     

  • 4π3

     

  • 5π3

     

(2)

Ans.     -π3

Explanation:

sin-1(-32)=sin-1(-sinπ3)

                         =-sin-1(sinπ3)=-π3



Q 23 :

The domain of the function defined by f(x)=sin-1x+cosx  is:

  • [-1,1]

     

  • [-1,π+1]

     

  • (-∞,∞)

     

  • ϕ

     

(1)

Ans.     [-1,1]

Explanation:

The domain of cosx is R and the domain of sin-1x is [-1,1].

∴  The domain of cosx+sin-1x is R∩[-1,1], i.e., [-1,1].



Q 24 :

The principal value of sec-1(-23) is:

  • 5π6

     

  • 2π3

     

  • π3

     

  • None of these

     

(1)

Ans.     5π6

Explanation:

sec-1(-23)=π-sec-1(23)

                        =π-π6=5π6



Q 25 :

If  sin-1x=y, then:

  • 0≤y≤x

     

  • -π2≤y≤π2

     

  • 0<y<π

     

  • -π2<y<π2

     

(2)

Ans.     -π2≤y≤π2

Explanation:

Range of  sin-1x is [-π2,π2]

∴                   -π2≤y≤π2



Q 26 :

The domain of the function cos-1(2x-1) is:

  • [0,1]

     

  • [-1,1]

     

  • (-1,1)

     

  • [0,π]

     

(1)

Ans.          [0, 1]

Explanation:

We know that cos-1x is defined for x∈[-1,1]

∴  f(x)=cos-1(2x-1) is defined if

                      -1≤2x-1≤1

⇒                    0≤2x≤2

⇒                    0≤x≤1



Q 27 :

The value of  cos-1(cos3π2) is equal to:

  • π2

     

  • 3π2

     

  • 5π2

     

  • 7π2

     

(1)

Ans.      π2

Explanation:

        cos-1(cos3π2)≠3π2  as  3π2∉[0,π]

∴   cos-1(cos3π2)=cos-1(0)=π2



Q 28 :

The value of sin[2sin-1(0.6)] is:

  • ·48

     

  • ·96

     

  • 1·2

     

  • sin 1·2

     

(2)

Ans.     ·96

Explanation:

Let sin-1(·6)=θ, i.e., sinθ=·6

Now,  sin[2sin-1(0.6)]=sin(2θ)=2sinθcosθ

                                                          =2(·6)(·8)=·96

            (∵ cosθ=1-sin2θ=1-(0.6)2=0.8)



Q 29 :

If cot-1(-15)=θ, the value of sinθ is:

  • 265

     

  • -526

     

  • 526

     

  • 526

     

(4)

Ans.      526

Explanation:

Given,    cot-1(-15)=θ,  where θ∈(0,π)

∴        cotθ=-15

∵        sinθ=1cosecθ=11+cot2θ

                    =11+(-15)2=11+125=12625

                    =526



Q 30 :

tan-13-sec-1(-2) is equal to:

  • π

     

  • -π3

     

  • π3

     

  • 2π3

     

(2)

Ans.     -π3

Explanation:

tan-13-sec-1(-2)

              =tan-13-(π-sec-12)

             =π3-π+sec-12

             =π3-π+π3

             =2π3-π

             =-π3



Q 31 :

The value of tan[12cos-1(53)] is:

  • 3+52

     

  • 3-52

     

  • -3+52

     

  • -3-52

     

(2)

Ans.    3-52

Explanation:

Let          y=tan[12cos-1(53)]

Putting,    x=cos-1(53)

⇒    cosx=53                         ...(i)

Now,        y=tan(x2)

⇒          y=1-cosx1+cosx

⇒         y=1-531+53                  [From (i)]

⇒         y=3-53+5=(3-5)(3-5)(3+5)(3-5)

⇒         y=(3-5)29-5=3-54

⇒          y=3-52

i.e.,   tan[12cos-1(53)]=3-52



Q 32 :

Match List I with List II.

  List I   List II
A. The range of sin-1x is I. [-π2,π2]-{0}
B. The range of tan-1x is II. (π2,π2)
C. The range of cosec-1x is III. [0,π]-{π2}
D. The range of sec-1x is IV. [-π2,π2]

 

Choose the correct answer from the option given below.

  • A-IV, B-III, C-II, D-I

     

  • A-IV, B-I, C-III, D-II

     

  • A-I, B-IV, C-II, D-III

     

  • A-IV, B-II, C-I, D-III

     

(4)

Ans.      A-IV, B-II, C-I, D-III



Q 33 :

If the equation x3+bx2+cx+1=0 (b<c) has only one real root α. Then the value of 2tan-1(cosec α)+tan-1(2sin α sec2 α) is:

  • -π2

     

  • -π

     

  • π2

     

  • π

     

(2)

x3+bx2+cx+1=0    

f(-1)=b-c<0    

f(0)=1>0    

B∈(0,1)

y=-2tan-1(cosecB)-tan-1(2sinBcos2B)

   =-(π+tan-12cosB1-cosec2B)-tan-12sinBcos2B

   =-π



Q 34 :

If ∑r=1n(tan2r-1cos2r)=tanpn-tanq, then find the value of (p+q)



(3)

∑r=1nsin(2r-2r-1)cos2rcos2r-1=∑r=1n(tan2r-tan2r-1)=tan2n-tan1



Q 35 :

Let p=tan(5π9cos(2sin-115)), q=sin-1(sin2π3)+cos-1(cos(7π6)) then the quadratic equation whose roots are p, sec q is (Here inverse trigonometric functions take principal values)

  • 3x2-x+3=0

     

  • 3x2-4x+23=0

     

  • 3x2-x-23=0

     

  • x2-3x+=0

     

(3)

cos(2sin-115)=35,  sin-1(sin2π3)=π3,   cos-1(cos7π6)=2π-7π6



Q 36 :

Exhaustive value of x such that cos-1(8x1+16x2)=-π2+2tan-1(4x)

  • (18,∞)

     

  • (116,18)

     

  • [14,∞)

     

  • (18,14)

     

(3)

On solving π2-sin-1(2×4x1+(4x)2)=-π2+2tan-1(4x)

⇒2tan-1(4x)=π-sin-1(2(4x)1+(4x)2)

4x≥1; x≥14



Q 37 :

Which of the following is true?

  • dydx for y=sin-1(cosx), where x∈(0,π), is -1

     

  • dydx for y=sin-1(cosx), where x∈(0,2π), is 1

     

  • dydx for y=cos-1(sinx), where x∈(-π,π2), is -1

     

  • dydx for y=cos-1(sinx), where x∈(-π2,3π2), is -1

     

(1)

Use graphs of sin-1(sinx) and cos-1(cosx)



Q 38 :

Let Sk=∑r=1ktan-1(6r22r+1+32r+1). Then limk→∞Sk is equal to

  • tan-1(32)

     

  • π2

     

  • cot-1(32)

     

  • tan-1(3)

     

(3)

Sk=∑r=1ktan-1(13(23)r(23)2r+1+1)=∑r=1k[tan-1(23)r-tan-1(23)r+1]=tan-1(23)r-tan-1(0)=cot-1(32)



Q 39 :

Let a1=1,a2,a3,a4,… be consecutive natural numbers. Then tan-1(11+a1a2)+tan-1(11+a2a3)+…+tan-1(11+a2024a2025) is equal to

  • π4+cot-1(2025)

     

  • tan-1(2025)-π4

     

  • tan-1(2024)-π4

     

  • π4-tan-1(2024)

     

(2)

By given condition, a2-a1=a3-a2=…=a2025-a2024=1

∴  tan-1(a2-a11+a1a2)+tan-1(a3-a21+a2a3)+…+tan-1(a2025-a20241+a2024a2025)

[tan-1a2-tan-1a1]+[tan-1a3-tan-1a2]+…+[tan-1a2025-tan-1a2024]

=tan-1a2025-tan-1a1=tan-1(2025)-π4



Q 40 :

Let [.] denote the greatest integer function. If the domain of the function f(x)=cos-1(4x+2[x]3) is [α,β], then 12(α+β) is equal to:        [2026]

  • 6

     

  • 8

     

  • 9

     

  • 4

     

(1)

We have,

y=cos-1(4x+2[x]3), then

-1≤4x+2[x]3≤1⇒-3≤4x+2[x]≤3

Case 1: If x∈[0,1], then -3≤4x≤3

∴   x∈[0,34]

Case 2: If x∈[1,2), then -3≤4x+2≤3⇒-5≤4x≤1

∴   x∈[-54,14]                 (Reject)

Case 3: If x∈[-1,0), then -3≤4x-2≤3⇒-1≤4x≤5

⇒x∈[-14,54]  ∴   x∈[-14,0]

Case 4: If x∈[-2,-1), then -3≤4x-4≤3⇒1≤4x≤7

∴  x∈[14,74]                    (Reject)

∴  Domain:x∈[-14,34]

Hence, α=-14, β=34

Thus, 12(α+β)=12(12)=6



Q 41 :

Let [·] denote the greatest integer function. If the domain of the function f(x)=sin-1(x+[x]3) is (α,β), then α2+β2 is equal to :           [2026]

  • 2

     

  • 5

     

  • 10

     

  • 13

     

(2)

Since, -1<sin-1θ<1

⇒-1≤x+[x]3≤1

⇒-3≤x+[x]≤3

⇒-3-[x]≤x≤3-[x]

If [x]=-1⇒x∈[-1,0)

If [x]=0⇒x∈[0,1)

If [x]=1⇒x∈[1,2)

Hence, x∈[-1,2)

⇒  α=-1 and β=2

So,   α2+β2=5



Q 42 :

Let 0<α<1, β=13α and tan-1(1-α)+tan-1(1-β)=π4. Then 6(α+β) is equal to:            [2026]

  • 6

     

  • 7

     

  • 8

     

  • 9

     

(2)

We have,

tan-1(1-α)+tan-1(1-β)=π4

⇒tan-1[(1-α)+(1-β)1-(1-α)(1-β)]=π/4

⇒1-α+1-β1-[1-α-β+αβ]=tanπ/4

⇒2-(α+β)α+β-αβ=1

⇒2-(α+β)=(α+β)-αβ

⇒2(α+β)=2+αβ     …(i)

∵  αβ=13    [∵Given]

∴  From (i),

α+β=2+132⇒α+β=76

⇒6(α+β)=7



Q 43 :

If sin(tan-1(x2))=cot(sin-11-x2), x∈(0,1), then the value of x is:           [2026]

  • 12

     

  • 13

     

  • 23

     

  • 58

     

(1)

Given

sin(tan-12x)=cot(sin-11-x2)

Let tan-12x=θ and sin-11-x2=ϕ

⇒2x=tanθ and sinϕ=1-x2

⇒sinθ=cotϕ

⇒2x1+2x2=x1-x2

⇒21-x2=1+2x2

Squaring both sides , we get

2-2x2=1+2x2

⇒1=4x2

⇒x=±12

∵  x∈(0,1)

So, x=12



Q 44 :

Let α=3sin-1(611) and β=3cos-1(49), where inverse trigonometric functions take only the principal values.

Given below are two statements :

Statement I : cos(α+β)>0.

Statement II : cos(α)<0.

In the light of the above statements, choose the correct answer from the options given below :             [2026]

  • Both Statement I and Statement II are true

     

  • Both Statement I and Statement II are false

     

  • Statement I is true but Statement II is false

     

  • Statement I is false but Statement II is true

     

(1)

12<611<12

⇒sin-1(12)<sin-1(611)<sin-1(12)

⇒π6<sin-1(611)<π4

⇒π2<3sin-1(611)<3π4

⇒π2<α<3π4     ∴ (cosα<0)   …(i)

Also, 0<49<12

⇒π3<cos-1(49)<π2

⇒π<3cos-1(49)<3π2

⇒π<β<3π2              …(ii)

From (i) and (ii), we get 3π2<α+β<9π4     ∴  cos(α+β)>0

So, both statement I and II are true.



Q 45 :

If π4+∑p=111tan-1(2p-11+22p-1)=α, then tanα is equal to ______ .            [2026]



(2048) 

Given,

π4+∑p=111tan-1(2p-11+22p-1)=α

Let,

Tp=tan-1(2p-11+22p-1)=tan-1(2p-2p-11+2p·2p-1)

=tan-1(2p)-tan-1(2p-1)

Now, T1=tan-1(21)-tan-1(20)

T2=tan-1(22)-tan-1(21)

T3=tan-1(23)-tan-1(22)

.................................................

T11=tan-1(211)-tan-1(210)

⇒∑p=111tan-1(2p-11+22p-1)=tan-1(211)-π4

∴  α=π4+tan-1(211)-π4

⇒tanα=211⇒tanα=2048