Q 1 :

Let α(a) and β(a) be the roots of the equation (1+a3-1)x2+(1+a-1)x+(1+a6-1)=0, 

where a>-1. Then lima→0+α(a)  and  lima→0+β(a) are     [2012]

  • -52 and 1

     

  • -12 and -1

     

  • -72 and 2

     

  • -92 and 3

     

(2)

(1+a3-1)x2+(1+a-1)x+(1+a6-1)=0

Let a+1=y, then equation reduces to

(y1/3-1)x2+(y1/2-1)x+(y1/6-1)=0

On dividing both sides by y-1, we get

(y1/3-1y-1)x2+(y1/2-1y-1)x+(y1/6-1y-1)=0

On taking limit as y→1  i.e.  a→0 on both sides, we get

13x2+12x+16=0 ⇒2x2+3x+1=0

⇒x=-1, -12 (roots of the equation)

∴  lima→0+α(a)=-1,    lima→0+β(a)=-12



Q 2 :

Let x0 be the real number such that ex0+x0=0. For a given real number α, define g(x)=3xex+3x-αex-αx3(ex+1) for all real numbers x. Then which one of the following statements is TRUE?             [2025]

 

  • For α=2, limx→x0|g(x)+ex0x-x0|=0

     

  • For α=2, limx→x0|g(x)+ex0x-x0|=1

     

  • For α=3, limx→x0|g(x)+ex0x-x0|=0

     

  • For α=3, limx→x0|g(x)+ex0x-x0|=23 

     

(3)

Given that ex0+x0=0

g(x)=3x(ex+1)-α(ex+x)3(ex+1)=x-α(ex+x)3(ex+1)limx→x0g(x)+ex0x-x0

=limh→0x0+h-α(ex0+h+x0+h)3(ex0+h+1)+ex0h               [∵ ex0+x0=0]

=limh→01-α(ex0+h-ex0+h)3h(ex0+h+1)

=limh→01-α3(ex0+h+1){ex0(eh-1)h+1}           [∵ limh→0eh-1h=1]

=1-α3(ex0+1)(ex0+1)=1-α3

So for α=2, required limit is 1-23=13

for α=3, required limit is 1-33=0



Q 3 :

If limx→∞(x2+x+1x+1-ax-b)=4, then                   [2012]

  • a=1, b=4

     

  • a=1, b=-4

     

  • a=2, b=-3

     

  • a=2, b=3

     

(2)

Given:  limx→∞(x2+x+1x+1-ax-b)=4

⇒limx→∞x2+x+1-ax2-ax-bx-bx+1=4

⇒limx→∞(1-a)x2+(1-a-b)x+(1-b)x+1=4

For this limit to be finite, 1-a=0⇒a=1

Then given limit reduces to:

limx→∞-bx+(1-b)x+1=4⇒limx→∞-b+(1-b)x1+1x=4

⇒-b=4 or  b=-4                               ∴  a=1,     b=-4



Q 4 :

If  limx→0((a-n)nx-tanx)sinnxx2=0, where n is a nonzero real number, then a is equal to                [2003]

  • 0

     

  • n+1n

     

  • n

     

  • n+1n

     

(4)

limx→0[(a-n)nx-tanx]sinnxx2=0

⇒limx→0n·sinnxnx[{(a-n)n-tanxx}]=0

⇒n·1·[(a-n)n-1]=0⇒(a-n)n-1=0

⇒a=1n+n               [∵  n is non zero real number]



Q 5 :

limx→0sin(πcos2x)x2 equals                          [2001]

  • -π

     

  • π

     

  • π2

     

  • 1

     

(2)

limx→0sin(πcos2x)x2=limx→0sin(π-πsin2x)x2

=limx→0sin(πsin2x)πsin2x×πsin2xx2=π



Q 6 :

The value of the limit limx→π242(sin3x+sinx)(2sin2xsin3x2+cos5x2)-(2+2cos2x+cos3x2) is ____________               [2020]



(8)

limx→π242·2sin2xcosx2sin2xsin3x2+(cos5x2-cos3x2)-2(1+cos2x)

=limx→π282·2sinxcosxcosx2sin2xsin3x2-2sin2xsinx2-22cos2x

=limx→π2162sinxcos2x2sin2x(sin3x2-sinx2)-22cos2x

=limx→π2162sinxcos2x4sinxcosx(2cosx.sinx2)-22cos2x

=162sinxcos2x2cos2x(4sinxsinx2-2)

=limx→π282sinx4sinx.sinx2-2=8



Q 7 :

Let m and n be two positive integers greater than 1. If limα→0(ecos(αn)-eαm)=-(e2), then the value of mn is                  [2015]



(2)

limα→0ecosαn-eαm=-e2

⇒limα→0e[ecosαn-1-1]cosαn-1×cosαn-1αm=-e2

⇒elimα→0-2sin2αn2(αn2)2×(αn2)2αm=-e2

⇒-e2α2n-m=-e2

⇒mn=2



Q 8 :

The largest value of non-negative integer a for which limx→1{-ax+sin(x-1)+ax+sin(x-1)-1}1-x1-x=14 is                   [2014]



(2)

limx→1{-ax+sin(x-1)+ax+sin(x-1)-1}1-x1-x=14

⇒limx→1{a(1-x)+sin(x-1)(x-1)+sin(x-1)}1+x

⇒limx→1{-a+sin(x-1)x-11+sin(x-1)x-1}1+x

⇒(-a+12)2=14

⇒a=0 or 2

∴  Largest value of a is 2.



Q 9 :

Let e denote the base of the natural logarithm. The value of the real number a for which the right hand limit limx→0+(1-x)1x-e-1xa is equal to a non-zero real number, is ________.                       [2020]



(1)

limx→0+(1-x)1/x-e-1xa=1=limx→0+e(ln(1-x)x)-1exa             [∵  (1-x)1/x=e1xln(1-x)]

=limx→0+1e·e(1+ln(1-x)x)-1xa=1elimx→0+ln(1-x)+xxa+1

=1elimx→0+(-x-x22-x33-⋯)+xxa+1

∴  a=1



Q 10 :

Let f(x)=1-x(1+|1-x|)|1-x|cos(11-x), for x≠1. Then               [2017]

  • limx→1-f(x)=0  

     

  • limx→1-f(x) does not exist

     

  • limx→1+f(x)=0  

     

  • limx→1+f(x) does not exist

     

Select one or more options

(1, 4)

Given:  f(x)=1-x(1+|1-x|)|1-x|cos(11-x), x≠1

limx→1-f(x)=limh→01-(1-h)(1+h)hcos(1h)

=limh→01-1+h2hcos(1h)=limh→0hcos(1h)=0

 limx→1+f(x)=limh→01-(1+h)(1+h)hcos(1h)

=limh→0-2h-h2hcos(1h)=limh→0(-2-h)cos(1h)

=-2×(some value oscillating between -1 and 1)

∴  limx→1+f(x) does not exist.



Q 11 :

For a∈ℝ (the set of all real numbers), a≠-1, limn→∞(1a+2a+⋯+na)(n+1)a-1[(na+1)+(na+2)+⋯+(na+n)]=160.

Then a=                         [2013]

  • 5

     

  • 7

     

  • -152

     

  • -172

     

Select one or more options

(2, 4)

Given:

limn→∞1a+2a+⋯+na(n+1)a-1[(na+1)+(na+2)+⋯+(na+n)]=160

⇒limn→∞na[(1n)a+(2n)a+⋯+(nn)a](n+1)a-1[n2a+n(n+1)2]=160

⇒limn→∞na-1(n+1)a-11n∑r=1n(rn)a[a+12(1+1n)]=160

⇒limn→∞(11+1n)a-11n∑r=1n(rn)aa+12(1+1n)=160

∵  1n∑r=1n(rn)a=∫01xadx  as  1n=dx and rn=x

when r=1, n→∞⇒x→0

when r=n⇒x→1

⇒∫01xadxa+12=160⇒[xa+1]01(a+1)(a+12)=160

⇒1(a+1)(a+12)=160

⇒2a2+3a-119=0⇒(a-7)(2a-17)=0

∴  a=7  or  -172



Q 12 :

Let f:R→R be a function. We say that f has

PROPERTY 1: If limh→0f(h)-f(0)|h| exists and is finite, and

PROPERTY 2: If limh→0f(h)-f(0)h2 exists and is finite.

Then which of the following options is/are correct?                     [2019]

  • f(x)=x2/3 has PROPERTY 1

     

  • f(x)=sinx has PROPERTY 2

     

  • f(x)=|x| has PROPERTY 1

     

  • f(x)=x|x| has PROPERTY 2

     

Select one or more options

(1, 3)

Property 1: limh→0f(h)-f(0)|h| exists and is finite

Property 2: limh→0f(h)-f(0)h2

(1) f(x)=x2/3 for Property 1

      limh→0h2/3-0|h|=limh→0|h|2/3|h|1/2=limh→0|h|1/6=0

      ∴    option (1) is correct.

(2)  f(x)=sinx for Property 2

      limh→0sinh-sin0h2=limh→0sinhh×1h  which does not exist.

      ∴  (2) is incorrect option.  

(3) f(x)=|x| for Property 1

      limh→0|h|-0|h|=limh→0|h|=0  

       ∴  option (3) is correct.  

(4) f(x)=x|x| for Property 2

      limh→0h|h|-0h2=limh→0|h|h  

    LHL =-1 and RHL =1

    ∴ limh→0|h|h   does not exist  

    ∴  option (4) is incorrect.