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11th And 12th > Mathematics

METHODS OF DIFFERENTIATION MCQs

Methods Of Differentiation

Total Questions : 55 | Page 6 of 6 pages
Question 51.


If f(x) = sin1(sin x)+cos1(sin x) and ϕ(x)=f(f(f(x))),then ϕ(x) is equal to


  1.     1
  2.     sin x
  3.     0
  4.     None of these
 Discuss Question
Answer: Option C. -> 0
:
C
f(x)=π2(a constant function)
ϕ(x)=0
Question 52.


If x2+y2=t1t and x4+y4=t2+1t2,then x3ydydx equals


  1.     - 1
  2.     0 
  3.     1
  4.     None of these
 Discuss Question
Answer: Option C. -> 1
:
C
x2+y2=t1t
On squaring both the sides
=x4+y4+2x2y2 = t2+1t22 
Given that -  
x4+y4=t2+1t2
x2y2=1
x2.2ydydx+y2.2x=0
x3ydydx=x2y2=1
Question 53.


If y=sin x+sin x+sin x+.....,then dydx is equal to


  1.     2y1cos x
  2.     cos x2y1
  3.     2x1cos x
  4.     cos x2x1
 Discuss Question
Answer: Option B. -> cos x2y1
:
B
y=sin x+yy2y=sin x
(2y1)dydx=cos x
Question 54.


If y=(1+cos 2 θ1cos2 θ),dydθ at θ=3π4 is


  1.     2
  2.     2
  3.     ±2
  4.     None of these
 Discuss Question
Answer: Option B. -> 2
:
B
y=(1+cos 2 θ1cos 2 θ)
=|cotθ|=cot θ(θ=3π4)
dydθ=cosec2θ
dydθ|θ=3π/4=(2)2=2
Question 55.


If (x2+y2)=a.etan1(y/x) a>0,then y"(0) is equal to


  1.     2aeπ/2
  2.    
    aeπ/2
  3.     2aeπ/2
  4.     Does not exist
 Discuss Question
Answer: Option C. -> 2aeπ/2
:
C
(x2+y2)=a.etan1(y/x)
12x2+y2(2x+2yy) =a.etan1(y/x)×11+y2x2×xyyx2.....(i)
x+yyx2+y2=(x2+y2)×xyyx2+y2
[from Eq.(i)]
x+yy=xyyy=x+yxy
y"=2(xyy)(xy)2
y"(0)=2(0y(0)){0y(0)}2=2aeπ/2=2aeπ/2

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