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All questions of Integration- Definite Integrals for A Level Exam

Evaluate: 
  • a)
    1/2
  • b)
    1/4
  • c)
    1
  • d)
    1/8
Correct answer is option 'B'. Can you explain this answer?

Sushil Kumar answered
Let I = ∫(0 to pi/2)x3 sin(tan−1x4)/(1+x8)dx
Put tan−1 x4 = t
4x3/(1+x8)dx = dt
⇒x3dx/(1+x8) = dt/4
Now, I = 1/4∫sin t dt
=−[1/4 cos t]0 to pi/2 + c
= -1/4[cos(0) - cos(pi/2)] +c
= 1/4[-cos(pi/2) + cos(0)] +c
= ¼[-0+1]
= 1/4 

Evaluate as limit of  sum 
  • a)
    20/5
  • b)
    15/2
  • c)
    20/3
  • d)
    3/20
Correct answer is option 'C'. Can you explain this answer?

Om Desai answered
 ∫(0 to 2)(x2 + x + 1)dx
= (0 to 2) [x3/3 + x2/2 + x]½
= [8/3 + 4/2 + 2]
 = 40/6
= 20/3

The value of the integral is:
  • a)
    2e – 1
  • b)
    2e + 1
  • c)
    2e
  • d)
    2(e – 1)
Correct answer is option 'D'. Can you explain this answer?

Correct Answer : d
Explanation :  ∫(-1 to 1) e|x| dx
∫(-1 to 0) e|x|dx + ∫(0 to 1) e|x|dx
 e1 -1 + e1 - 1
=> 2(e - 1)

  • a)
    -1
  • b)
    zero
  • c)
    1
  • d)
    2
Correct answer is option 'B'. Can you explain this answer?

Praveen Kumar answered
∫(0 to 4)(x)1/2 - x2 dx
= [[(x)3/2]/(3/2) - x2](0 to 4)
= [[2x3/2]/3 - x2](0 to 4)
= [[2(0)3/2]/3 - (0)2]] -  [[2(4)3/2]/3 - (4)2]]
= 0-0
= 0

If   is
  • a)
    2/3
  • b)
    4/5
  • c)
    1
  • d)
    None of these
Correct answer is option 'B'. Can you explain this answer?

Om Desai answered
In the question, it should be f’(2) instead of f”(2) 
Explanation:- f(x) = ∫(0 to x) log(1+x2)
f’(x) = 2xdx/(1+x2)
f’(2) = 2(2)/(1+(2)2)
= 4/5

The value of  is:​
  • a)
    π/2
  • b)
    1
  • c)
    π/4
  • d)
    π
Correct answer is option 'C'. Can you explain this answer?

Praveen Kumar answered
1 + tan2 x = sec2 x
∫(π/2 to π/4)(sec2 x)/(1 + tan2 x)
=> ∫(π/2 to π/4)(sec2 x)/(sec2 x) dx
= ∫1(π/2 to π/4) dx
= [x](π/2 to π/4)
= π/2 - π/4  =  π/4 

  • a)
  • b)
  • c)
  • d)
Correct answer is option 'D'. Can you explain this answer?

Sushil Kumar answered
Option d is correct, because it is the property of definite integral
 ∫02a f(x) dx = ∫0a f(x) dx + ∫0a f(2a – x) dx

Find   
  • a)
    π/4
  • b)
    π/2
  • c)
  • d)
Correct answer is option 'B'. Can you explain this answer?

Vivek Patel answered
Using trigonometric identities, we have
cos2x=cos2x-sin2x  -(1) and cos2x+sin2x =1 -(2)
cos2x=1-sin2x , substituting this in equation (1) we get 
cos2x=1-sin2x-sin2x=1-2sin2x
So,cos2x=1-2sin2x
2sin2x=1-cos2x


 

  • a)
    π
  • b)
    π/2
  • c)
  • d)
    π/4
Correct answer is option 'B'. Can you explain this answer?

Tarun Kaushik answered
For sin2(X), we will use the cos double angle formula:
cos(2X) = 1 - 2sin2(X)
The above formula can be rearranged to make sin2(X) the subject:
sin2(X) = 1/2(1 - cos(2X))
You can now rewrite the integration: 
∫sin2(X)dX = ∫1/2(1 - cos(2X))dX
Because 1/2 is a constant, we can remove it from the integration to make the calculation simpler. We are now integrating:
1/2 x ∫(1 - cos(2X)) dX 
= 1/2 x (X - 1/2sin(2X)) + C]-pi/4 to pi/4
∫sin2(X) dX = [1/2X - 1/4sin(2X)]-pi/4 to pi/4 + C
½[-pi/2] - 1/4sin(2(-pi/4)] - ½[pi/2] - 1/4sin(2(pi/4)] 
= π/2

The value of  is:
  • a)
    10
  • b)
    17/2
  • c)
    7/2
  • d)
    5
Correct answer is option 'A'. Can you explain this answer?

Sushil Kumar answered
∫(-3 to 3) (x+1)dx
=  ∫(-3 to -1) (x+1)dx +  ∫(-1 to 3) (x+1) dx 
= [x2 + x](-3 to -1) + [x2 + x](-1 to 3)
= [½ - 1 - (9/2 - 3)] + [9/2 + 3 - (½ - 1)]
= -[-4 + 2] + [4 + 4]
= -[-2] + [8]
= 10

If   then the value of k is:
  • a)
    7/8
  • b)
    5/8
  • c)
    1/2
  • d)
    3/2
Correct answer is option 'C'. Can you explain this answer?

Sushil Kumar answered
Let I=∫(0 to k) 1/[1 + 4x2]dx = π8
Now, ∫(0 to k) 1/[4(1/4 + x2)]dx
= 2/4[tan−1 2x]0 to k
= 1/2tan-1 2k − 0 = π/8
1/2tan−1 2k = π8
⇒ tan−1 2k = π/4
⇒ 2k = 1
∴ k = 1/2

  • a)
    – log (1+ex)
  • b)
    log (1+e−x)
  • c)
    log(e−x+1)
  • d)
    none of these
Correct answer is option 'A'. Can you explain this answer?

Divya Menon answered
ANSWER :- a
Solution :- Let e^x/2 = tanθ. Then 1/2e^(x/2)dx = sec^2θdθ.
∫dx/(e^x+1)     = 2∫½ e^(x/2)dx/[e^(x/2)(e^x+1)]
= 2∫[sec^2θdθ]/tanθ(sec^2θ)
= 2∫cosθ/sinθ)dθ = 2ln |sinθ|
From tanθ = e^(x/2) draw a right triangle to see that sinθ = e^x/2√e^x+1:
= 2ln∣e^pi/2√(e^x + 1)|
= ln |e^x/(e^x+1)|
= x−ln(e^x+1)+ C

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