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12th Grade > Mathematics

LIMITS CONTINUITY AND DIFFERENTIABILITY MCQs

Total Questions : 45 | Page 2 of 5 pages
Question 11. If f(9) = 9, f'(9) = 4, then limx9f(x)3x3 equals 
  1.    2
  2.    4
  3.    6
  4.    0
 Discuss Question
Answer: Option B. -> 4
:
B
Given that f(9) = 9, f’(9) = 4
limx9f(x)3x3
On rationalisation we get -
=limx9(f(x)3x3)(x+3x+3)(f(x)+3f(x)+3)
=limx9f(x)f(9)x9 .66
=limx9f(x)f(9)x9
=f(9)
=4
Question 12. If f(x)={sinx,xnπ,nϵI2,otherwise and g(x)=x2+1,x0,24,x=05,x=2, then limx0g{f(x)}
  1.    5
  2.    6
  3.    7
  4.    1
 Discuss Question
Answer: Option D. -> 1
:
D
limx0g{f(x)}=limx0(f(x))2+1,f(x)0,24,f(x)=05,f(x)=2=limx0















sin2x+1,sinx0,2andxnπ4,sinx=0andxnπ5,sinx=2andxnπ5,20,2andxnπ4,2=0andx=nπ5,2=2andx=nπ
=limx0{1+sin2x,xnπ5,x=nπ=1+sin20=1+0=1
Question 13. Let f(x)={x2k(x24)2xwhen x is an int eger otherwise then limx2f(x)
  1.    exists only when k=1
  2.    exists for every real k
  3.    exists for every real k = 1
  4.    does not exist
 Discuss Question
Answer: Option B. -> exists for every real k
:
B
limx2+f(x)=limx2+k(x24)2x=limx2+k(2x)=4klimx2+f(x)=limx2+k(x24)2x=limx2k(2x)=4k
Hence limits exists for every real value of k.
Question 14. limx01cos 3xx(3x1)=
  1.    92
  2.    9(2log3)
  3.    9log32
  4.    1 
 Discuss Question
Answer: Option B. -> 9(2log3)
:
B
limx01cos3xx(3x1)
cos3x=19x22!+
1cos3x=9x22!+ ......... (1)
limx03x1x=log3 .......... (2)
limx01cos3xx2(3x1x)
From (1) and (2) we get
=92log3
Question 15. The value of limx1[sin sin1x] is 
  1.    1
  2.    does not exist
  3.    π2
  4.    0
 Discuss Question
Answer: Option A. -> 1
:
A
Since x1 means x1-, sin-1 x is not defined for x>1
limx1[sinsin1x]=limx1[sinsin1x]=1
Question 16. limx2x2+x2x24is equal to
  1.    1/2
  2.    1
  3.    2
  4.    -1
 Discuss Question
Answer: Option A. -> 1/2
:
A
=limx2{1x+2+x2x24}Limit=12+limx2x2x+21(x+2)(x2)=12+limx21x+2x2x+2=12
Question 17. If limx0(1+asinx)cosecx=3, then a is 
  1.    In 2
  2.    In 3
  3.    In 4
  4.    e3
 Discuss Question
Answer: Option B. -> In 3
:
B
3=limx0(1+asinx)cosecx
[1form]limx0ecosecx.asinx=ea
ea=3a=loge3=ln3.
Question 18. Which of the following limit is not in the indeterminant form ?
  1.    limx→ax3−a3x−a
  2.    limx→asin x cosec x
  3.    limx→0xx
  4.    limx→00x
 Discuss Question
Answer: Option D. -> limx→00x
:
D
limxax3a3xa=(00inderminant form)
limxasinxcosecx=(0×inderminant form)
limxaxx=(00inderminant form)
limxa0x=0(not inderminant form)
Question 19. The value oflimx01cos3xxsin xcosx
  1.    2/5
  2.    3/5
  3.    3/2
  4.    3/4
 Discuss Question
Answer: Option C. -> 3/2
:
C
limx01cos3xxsinxcosx=limx0(1cosx)(1+cosx+cos2x)xsinxcosx=limx02sin2(x2)2sin(x2)cos(x2).x×(1+cosx+cos2x)cosx=limx0sin(x2)2(x2)×1+cosx+cos2xcos(x2)cosx=12×3=32
Question 20. limnn.cos(π4n).sin(π4n) is equal to 
  1.    π4 
  2.    π6 
  3.    π9 
  4.    π3 
 Discuss Question
Answer: Option A. -> π4 
:
A
limxn.cos(π4n)sin(π4n)
=limnn2sinπ2n
=π4

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