All questions of Integrals for Mathematics Exam

If the triple integral over the region bounded by the planes 2x + y + z = 4, x = 0,  y = 0, z = 0 is given by then the function λ(x) – π(x, y) is 
  • a)
    y
  • b)
    x
  • c)
    x + y 
  • d)
    x – y 
Correct answer is option 'A'. Can you explain this answer?

Veda Institute answered
where V is region bounded by the plane 2x + y + z = 4 x = 0, y = 0, z = 0


From (1) & (2), we have
⇒ λ(x) = 4 – 2x.
µ(x, y) = 4 – 2x – y
⇒ λ – µ = 4 – 2x – 4 + 2x + y = y.

Consider the shaded triangular region P shown in the figure. What is xy dxdy?
  • a)
    1/6
  • b)
    2/9
  • c)
    1/16
  • d)
    1
Correct answer is option 'A'. Can you explain this answer?

Chirag Verma answered
The intercept form of equation is


where, a is x intercept and b is y intercept.
So Given, equation is 
implies x+2y=2
implies x=2(1 - y)
Limit of x is form 0 to 2(1 - y ) and limit of y is from 0 to 1.
Therefore, 

= 1/6
 

The value of integral dxdy is
  • a)
  • b)
    √π
  • c)
    π
  • d)
    π/4
Correct answer is option 'D'. Can you explain this answer?

Veda Institute answered
I = dxdy

Putting x+ y2 = r2, we get
Limits of  r = 0 to ∞
and 0 = θ to π/2
Now, Putting r2 = t, we get

The area bounded by the curves y2 = 9x, x —y + 2 = 0 is given by
  • a)
    1
  • b)
    1/2
  • c)
    3/2
  • d)
    5/4
Correct answer is option 'B'. Can you explain this answer?

Veda Institute answered
The equations of the given curves are

y2 = 9x
x - y + 2 = 0
The curves (/') and (ii) intersect at
A(1, 3) and B(4, 6)
So, the required area

= 1/2
 

Let f(x) =  then f decrease in the interval (x1, x2)
  • a)
  • b)
    ( - 2 , - 1 )
  • c)
    ( 1 ,2 )
  • d)
Correct answer is option 'C'. Can you explain this answer?

Vikram Kapoor answered
f(x) = ∫ex(x−1)(x−2)dx
For decreasing function ,f′(x)<0,f′(x)<0
⇒ex(x−1)(x−2) < 0
⇒(x−1)(x−2) < 0
⇒ ex(x−1)(x−2) < 0
⇒ (x−1)(x−2) < 0
⇒1 < x < 2,
∵ e> 0 ∀ x ∈ R

The integral is equal to
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'C'. Can you explain this answer?

Veda Institute answered
The given integral is


From above triple integral, the projection in yz-plane is y = 0, y = 1 – z & z = 0, z = 1

So, the above integral can be rewrite as

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

Veda Institute answered
Step 1: Simplify by Changing Variables
To simplify this integral, note that we can use the property of separable integrals by changing variables. However, for clarity, let’s proceed with evaluating the inner integral directly.
Step 2: Evaluate the Inner Integral with Respect to x

Step 3: Integrate with Respect to y

Conclusion: The value of the integral is: 2.
So, the correct answer is: D: 2.

The area bounded by the parabola y2 = 4ax and straight line x + y = 3a is
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'D'. Can you explain this answer?

Veda Institute answered
We need to find the area bounded by the parabola y² = 4ax and the straight line x + y = 3a.
Step 1: Rewrite the Equations
The given equations are:
  • Parabola: y² = 4ax
  • Line: x + y = 3a, which can be rewritten as y = 3a - x
Step 2: Find Points of Intersection
To find the intersection points, substitute y = 3a - x into y² = 4ax:
(3a - x)² = 4ax.
Expanding and simplifying:
9a² - 6ax + x² = 4ax,
x² - 10ax + 9a² = 0.
This is a quadratic equation in x:
(x - 5a)² = 0.
So, x = 5a. Substituting x = 5a back into y = 3a - x:
y = 3a - 5a = -2a.
Thus, the point of intersection is (5a, -2a).
Step 3: Set Up the Integral for the Area
To find the area bounded by the parabola and the line, we integrate horizontally from x = 0 to x = 5a, finding the difference between the y-values of the line and the parabola at each x.
The area A is given by:
A = ∫05a ((3a - x) - √(4ax)) dx.
Step 4: Evaluate the Integral
We will split the integral into two parts:
1. Integral of (3a - x):
2. Integral of √(4ax):
Rewrite √(4ax) = 2√(ax), so we have:

Conclusion:
The correct answer, after calculating both integrals, is:
D: 10a² / 3.

 Find the value of ∫∫xyex + y dxdy.
  • a)
    yey (xex-ex)
  • b)
    (yey-ey)(xex-ex)
  • c)
    (yey-ey)xex
  • d)
    (yey-ey)(xex+ex)
Correct answer is option 'B'. Can you explain this answer?

Chirag Verma answered
Add constant automatically
Explanation: Given, ∫∫xyex + y dxdy
∫∫xyex ey dxdy= ∫yey dy∫xex dx=(yey-ey)(xex-ex).

By changing the order of integration in the value is
  • a)
    π/4
  • b)
    πa/4
  • c)
    πa
  • d)
    a/4
Correct answer is option 'B'. Can you explain this answer?

Veda Institute answered
To evaluate the integral:
0a ∫ya (x / (x² + y²)) dx dy
by changing the order of integration, we need to determine the region of integration in the x-y plane and then rewrite the integral accordingly.
Step 1: Determine the Region of Integration
The given limits indicate that:
  • y ranges from 0 to a,
  • For a fixed yx ranges from y to a.
In the x-y plane, this describes the triangular region bounded by:
  • y = 0,
  • x = a,
  • x = y.
Step 2: Change the Order of Integration
To change the order of integration, we need to describe the region in terms of x first:
  • x ranges from 0 to a,
  • For a fixed xy ranges from 0 to x (since y ≤ x within this region).
Thus, we can rewrite the integral as:
Step 3: Evaluate the Inner Integral with Respect to y
Now, we evaluate the inner integral:
Since x is treated as a constant in the inner integral, we can factor it out:
Integrate with respect to y:
Since arctan(1) = π/4 and arctan(0) = 0, this becomes:
= (1/x) * (π/4) = π / (4x).
Step 4: Substitute Back and Integrate with Respect to x
Now our integral becomes:
This simplifies to:
Conclusion:
The value of the integral is:
B: πa / 4.

rdθdr is given by
  • a)
    sinθdθ
  • b)
    1/2 πrdr
  • c)
    1/2 sin2θdθ
  • d)
    None of these
Correct answer is option 'C'. Can you explain this answer?

Veda Institute answered

The equations of given curves are
y(x2 + 2) = 3x
and 4y = x2
The curve (i) and (ii) intersect at A(2,1). 

The volume of the tetrahedron bounded by the plane  and the co-ordinate planes is equal to
  • a)
    1/3 πabc
  • b)
    2/3 πabc
  • c)
    1/6 πabc
  • d)
    None of these
Correct answer is option 'D'. Can you explain this answer?

Chirag Verma answered
Here
Let u = x/a, v = y/b , w = z/c
Then dx = a du, dy = b dv, dz = c dw
So, Required volume
V = abc du dv dw
where u + v + w ≤ 1, u ,v ,w ≥ 0
Thus 

Hence, the correct answer is (c)

  • a)
    cot x – x + C
  • b)
    -cot x – x + C
  • c)
    cot x + x + C
  • d)
    -cot x + x + C
Correct answer is option 'B'. Can you explain this answer?

Chirag Verma answered
We know that cot2 x = cosec2x – 1
∫cot²x dx = ∫ (cosec2x – 1) dx = -cot x -x + C. [Since, ∫cosec2x dx = -cot x + c]
Hence, the correct answer is option (b) -cot x – x + C.

 is equal to
  • a)
     esin^2y
  • b)
    sin2y esin2y
  • c)
    0
  • d)
    none of these
Correct answer is option 'A'. Can you explain this answer?

Veda Institute answered
ANSWER :- A
Solution :- limx→0 1/x[∫y→a e^sin2tdt− ∫x+y→a e^sin2tdt]
 limx→0  [∫y→a e^sin2tdt− ∫x+y→a e^sin2tdt]/x
Hence it is 0/0 form, Apply L-hospital rule.
lim x-->0  0 - {e^(sin^2a).0 - e^(sin^2(x+y).1}/1
lim x-->0 e^(sin^2(x+y))
= e^(sin^2y)

The volume of the cylinder x2 + y2 = a2 bounded below by z = 0 and bounded above by z = h is given by 
  • a)
    πah
  • b)
    πa2h
  • c)
    1/3πa3h
  • d)
    None of these 
Correct answer is option 'B'. Can you explain this answer?

Chirag Verma answered
The equation of the cylinder is
x2 + y2 = a2
The equation of surface CDE is z = h
So, the required volume is


Let x = a sin θ
implies dx = a cosθ dθ
So, volume V

Changing the order of integration in the double integral leads to, then the value of q is
  • a)
    4y
  • b)
    x
  • c)
    16y2
  • d)
    8
Correct answer is option 'A'. Can you explain this answer?

Veda Institute answered
Given, I =  
Equation of the line is x = Ay Starting val ue of x is zero and final value of x is 8 but we want the result of first integration in terms of y, so that we can integrate the result with respect to y to get the final result. So, limits are from 0 to 4y.
And integration limit for y is from 0 to 2.

So, 

Hence, r=0, s=2, p=0, q=4y

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