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12th Grade > Mathematics

LIMITS CONTINUITY AND DIFFERENTIABILITY MCQs

Total Questions : 45 | Page 4 of 5 pages
Question 31. The value of limx0xa[bx] is, ([.]G.I.F)
  1.    0
  2.    ∞
  3.    ba 
  4.    does not exist
 Discuss Question
Answer: Option C. -> ba 
:
C
limx0xa[bx]
=limx0xa(bx{bx})
Since {bx}ϵ[0,1)
=limx0xa.{bx}=0
limx0xa[bx]=limx0(xa)(bx)
=limx0.ba
=ba
Question 32. limx02sinxsin2xx3 is equal to 
  1.    1
  2.    −1
  3.    0
  4.    does not exist
 Discuss Question
Answer: Option A. -> 1
:
A
limx02sinxsin2xx3
=limx02sinx(1cosx)(1+cosx)x3(1+cosx)
=limx02sin3xx3×11+cosx
=2×(1)3×11+1=1
Question 33. The value of limxx+cos xx+sin xis
  1.    -1
  2.    0
  3.    1
  4.    2
 Discuss Question
Answer: Option C. -> 1
:
C
limxx+cosxx+sinx[Puttingx=1h;asx,h0]=limh01h+cos(1h)1h+sin(1h)=limh01+hcos1h1+hcos1h=1+01+0

1sin1h1and1cos1h1,whereh0,hcos1h0andhsin1h0

=1
Question 34. If limx0kx cosec x = limx0x cosec kx , then k =
  1.    1
  2.    -1
 Discuss Question
Answer: Option C. -> 1
:
C
limx0kx cosec x = limx0 x cosec kx
= k limx0xsinx =1klimx0kxsinkx =k=1k=k=± 1
Question 35. limx0tan1xsin1xx3is equal to
  1.    1/2
  2.    -1/2
  3.    1
  4.    -1
 Discuss Question
Answer: Option B. -> -1/2
:
B
limx0tan1xsin1xx3(00form)limx011+x211x23x2limx01x2(1+x2)3x2(1+x2)1x2limx0(1x2)(1+x2)23x2(1+x2)1x2[1x2+(1+x2)]=36=12
Question 36. limx0(1+x)13(1x)13x=
  1.    2/3
  2.    1/3
  3.    1
  4.    0
 Discuss Question
Answer: Option A. -> 2/3
:
A
limx0(1+x)13(1x)13x=limx0(1+x)13(1x)13(1+x)(1x).2=2.13
Question 37. ABC is an isosceles triangle inscribed in a circle of radius r. If AB = AC and h is the altitude from A to BC.The triangle ABC has perimeter P=2[(2hrh2)+2hr] and A be the area of the triangle .Find limh0AP3  
  1.    1r
  2.    164r
  3.    1128r
  4.    12r
 Discuss Question
Answer: Option C. -> 1128r
:
C
ABC Is An Isosceles Triangle Inscribed In A Circle Of Radius...
In ABC,AB=AC
ADBC(DismidpointofBC)
Let r = radius of circumcircle
OA = OB = OC = r
Now BD = BO2OD2
=r2(hr)2=2rhh2
BC=22rhh2
Area of ABC= 12×BC×AD
=h2rhh2
Also limh0Ap3=h2rhh28(2rhh2+2hr)3
=limh0h3/22rh8h3/2(2rh+2r)3
=limh02rh8[2rh+2r]3
=2r8(2r+2r)3=2r8.8.2r2r=1128r
Question 38. Let f  be a function such that f(x+y)=f(x)+f(y)  for all x  and y  and f(x)=(2x2+3x)g(x) for all x  where g(x)  is continuous and g(0)=9  then f'(0)  is equals to
 
  1.    9
  2.    3
  3.    27
  4.    6
 Discuss Question
Answer: Option C. -> 27
:
C
f(x)=limh0f(x+h)f(x)h
=limh0f(x)+f(h)f(x)h
=limh0(2h2+3h)g(h)h
=limh0(2h+3)g(h)
=3g(0)
=27
Question 39. The values of constants a and b so thatlimx(x2+1x+1axb)=12,are
  1.    a=1,b=−32
  2.    a=−1,b=32
  3.    a=0, b=0
  4.    a =2, b= -1
 Discuss Question
Answer: Option A. -> a=1,b=−32
:
A
limx(x2+1x+1axb)=12limx(x2+1)(ax+b)(x+1)x+1=12limxx2(1a)(a+b)xb+1x+1=121a=0anda+b=12a=1b=32
Question 40. If the derivative of the function f(x)=bx2+ax+4;x1ax2+b;x<1, is everywhere continuous, then
  1.    a = 2, b = 3
  2.    a = 3, b = 2
  3.    a = - 2, b = - 3
  4.    a = - 3, b = - 2
 Discuss Question
Answer: Option A. -> a = 2, b = 3
:
A
Wehave,f(x)={ax2+b,x<1bx2+ax+4,x1f(x)={2ax,<12bx+a,x1Since,f(x)isdifferentiableatx=1,thereforeitiscontinuousatx=1andhence,limx1f(x)=limx1+f(x)a+b=ba+4a=2andalso,limx1f(x)=limx1+f(x)2a=2b+a3a=2bb=3(a=2)Hence,a=2,b=3

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