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All questions of Chapter 8 - Application of Integrals for JEE Exam

The area shaded in the given figure can be calculated by which of the following definite integral?
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'D'. Can you explain this answer?

Leelu Bhai answered
The required area is calculated by the difference of area of upper curve and lower curve.Now equation of upper curve 
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The area of the region bounded by y = x2 – 2x and y = 4 – x2 is.​
  • a)
    7 sq. units
  • b)
    8 sq. units
  • c)
    9 sq. units
  • d)
    10 sq. units
Correct answer is option 'C'. Can you explain this answer?

Vikas Kapoor answered
To find area between y = x2 – 2x and y = 4 – x2,
We need to find POI.
x2 – 2x = 4 – x2
2x2 - 2x – 4 = 0
x2 – x – 2 = 0
(x-2)(x+1) = 0
x = -1, 2


= [(-2x3)/3 + x2 + 4x]x=2 - [(-2x3)/3 + x2 + 4x]x= -1
= -16/3 + 4 + 8 – (2/3 + 1 - 4)
= 9 sq units

Let f : [0, ∞)→ R be a continuous and strictly increasing function such that  The area enclosed by y = f (x), the x-axis and the ordinate at x = 3, is
  • a)
    1
  • b)
    3/2
  • c)
    2
  • d)
    3
Correct answer is option 'B'. Can you explain this answer?

Om Desai answered
Given, f3(x) = ∫(0 to x)tf(t)dt
Differentiating throughout w.r.t x,
3f2(x) f′(x) = xf2(x)
⇒ f′(x)= x/3
​So, f(x)=∫(0 to x) x/3 dx = (x2)/6
Area = ∫f(x)dx=∫(0 to 3) (x2)/6 dx
= {(x3)/18}(0 to 3)
= 3/2

The area between the curves y = x2 and y = x3 is:​
  • a) 
    1/12 sq.units
  • b) 
    1/8 sq.units
  • c) 
    1/10 sq.unit
  • d) 
    1/6 sq.units
Correct answer is option 'A'. Can you explain this answer?

Arun Khanna answered
First we note that the curves intersect at the points (0,0) and (1,1).  Then we see that

        x^3  <  x^2  

in this interval.  Hence the area is given by
         
  = 1/3 - 1/4 = 1/12.

The area bounded by the curves y = x2, y = [x+1], x < 1 and the y - axis, where[.] denotes the greatest integer not exceeding x, is
  • a)
    2/3
  • b)
    1/3
  • c)
    1
  • d)
    2
Correct answer is option 'A'. Can you explain this answer?

Snehal Mehta answered
To find the area bounded by the given curves, we need to determine the points of intersection between the curves and the boundaries of the region.

1. Finding the point of intersection:
Let's first find the point of intersection between the curves y = x^2 and y = [x].

For y = x^2, we have:
x^2 = [x]

To find the intersection points, we need to consider two cases:
Case 1: When x is an integer
In this case, [x] will be equal to x. So, the equation becomes:
x^2 = x
x^2 - x = x(x - 1) = 0
This gives us two solutions: x = 0 and x = 1.

Case 2: When x is not an integer
In this case, [x] will be equal to the greatest integer less than or equal to x. So, the equation becomes:
x^2 = x - 1
x^2 - x + 1 = 0
Using the quadratic formula, we can solve for x, but we can see that the discriminant (b^2 - 4ac) is negative, which means there are no real solutions.

Therefore, the only points of intersection are (0, 0) and (1, 1).

2. Determining the boundaries of the region:
The given boundaries are y = [x], y = 0, and x = 1.

Since y = [x] represents the greatest integer less than or equal to x, it means that y will be an integer for all values of x between two consecutive integers. Therefore, the boundary y = [x] is equivalent to y = 0 for x < 1="" and="" y="1" for="" 1="" ≤="" x="" />< />

3. Calculating the area:
The area bounded by the curves can be divided into two regions:

Region 1: Bounded by y = x^2, y = 0, and x = 1
This region is a right-angled triangle with base 1 and height 1 (the point of intersection (1, 1)). Therefore, the area of this region is 1/2 * base * height = 1/2 * 1 * 1 = 1/2.

Region 2: Bounded by y = x^2, y = 1, and x = 2
This region is a trapezium with bases of lengths 2 and 1 (the points of intersection (0, 0) and (1, 1)). The height of the trapezium is 1 (the difference between the y-coordinates of the points of intersection). Therefore, the area of this region is 1/2 * (base1 + base2) * height = 1/2 * (2 + 1) * 1 = 3/2.

Total area = Area of Region 1 + Area of Region 2 = 1/2 + 3/2 = 2/3.

Therefore, the correct answer is option A, 2/3.

The area bounded by [x] +[y] = 8 such that x, y > 0 is .... sq. units
Where [.] is G.I.F.
  • a)
    3
  • b)
    6
  • c)
    9
  • d)
    12
Correct answer is option 'C'. Can you explain this answer?

Jaya Das answered
Given Equation:
The equation of the line is given as [x] + [y] = 8. Here, [.] denotes the greatest integer function.

Finding the Area:
To find the area bounded by this equation, we need to visualize the region formed by the line [x] + [y] = 8 in the first quadrant where x and y are greater than or equal to 0.

Understanding the Region:
The line [x] + [y] = 8 passes through the points (8,0) and (0,8). This line divides the first quadrant into two regions.
One region is a triangle with vertices at (0,0), (8,0), and (0,8). The area of this triangle is 1/2 * base * height = 1/2 * 8 * 8 = 32 sq. units.
The other region is a square with side length 8 units. The area of this square is 8 * 8 = 64 sq. units.

Calculating the Bounded Area:
The area bounded by the line [x] + [y] = 8 in the first quadrant is the sum of the areas of the triangle and the square, which is 32 + 64 = 96 sq. units.
Therefore, the area bounded by [x] + [y] = 8 such that x, y are greater than or equal to 0 is 96 sq. units.

Conclusion:
The correct option is (C) 9 sq. units.

The area bounded by the curve y = 2x - x2 and the line x + y = 0 is
  • a)
    9/2 sq. units
  • b)
    35/6 sq. units
  • c)
    19/6 sq. units
  • d)
    none of these
Correct answer is option 'A'. Can you explain this answer?

Pranav Pillai answered
The equation y = 2x − x2 i.e. y – 1 = - (x - 1)2 represents a downward parabola with vertex at (1, 1) which meets x – axis where y = 0 .i .e . where x = 0 , 2. Also , the line y = - x meets this parabola where – x = 2x − x2 i.e. where x = 0 , 3. 
Therefore , required area is :

Area of the region bounded by the curves y = ex, x = a , x = b and the x- axis is given by
  • a)
    eb−ea
  • b)
    eb−a
  • c)
    eb+ea
  • d)
    none of these
Correct answer is option 'A'. Can you explain this answer?

Nisha Sen answered
To find the area of the region bounded by the curves y = ex, x = a, x = b, and the x-axis, we can use integration.

Step 1: Determine the limits of integration
The region is bounded by the vertical lines x = a and x = b, so the limits of integration for x will be from a to b.

Step 2: Set up the integral
The area of the region can be found by integrating the function y = ex with respect to x over the given limits of integration.

The integral for the area is given by:
∫(ex) dx from a to b

Step 3: Evaluate the integral
Integrating the function ex with respect to x gives us ex.

So, the integral becomes:
∫(ex) dx = ex

Evaluating this integral from a to b gives us:
ex evaluated from a to b = eb - ea

Step 4: Subtracting the areas below the x-axis
Since the region is bounded by the x-axis, we need to consider the areas below the x-axis as negative.

If there are any values of x within the interval (a, b) where ex is negative, we need to subtract the absolute value of the integral of ex in that range. However, since the function ex is always positive, we don't need to consider this step.

Step 5: Finalize the answer
The area of the region bounded by the curves y = ex, x = a, x = b, and the x-axis is given by:
Area = eb - ea

Therefore, the correct answer is option A) eb - ea.

The area of the part of circle x2 + y2 - 2x - 4y -1 = 0 above 2x - y = 0 is ...... sq. units
  • a)
     3π
  • b)
  • c)
  • d)
    π
Correct answer is option 'A'. Can you explain this answer?

Nandini Kumar answered
To find the area of the part of the circle above the line, we first need to determine the points of intersection between the circle and the line.

1. Finding the points of intersection:
We have two equations:
- Circle equation: x^2 + y^2 - 2x - 4y - 1 = 0
- Line equation: 2x - y = 0

To find the points of intersection, we can substitute the value of y from the line equation into the circle equation:
x^2 + (2x)^2 - 2x - 4(2x) - 1 = 0
x^2 + 4x^2 - 2x - 8x - 1 = 0
5x^2 - 10x - 1 = 0

Using the quadratic formula, we can solve for x:
x = (-b ± √(b^2 - 4ac)) / (2a)
where a = 5, b = -10, and c = -1.

Calculating the values of x using the quadratic formula, we get:
x = (-(-10) ± √((-10)^2 - 4(5)(-1))) / (2(5))
x = (10 ± √(100 + 20)) / 10
x = (10 ± √120) / 10
x = (10 ± 2√30) / 10
x = 1 ± 0.632

So, the two x-values of intersection are x = 1.632 and x = 0.368.

Now, substitute these x-values back into the line equation to find the corresponding y-values:
For x = 1.632: 2(1.632) - y = 0
y = 3.264
For x = 0.368: 2(0.368) - y = 0
y = 0.736

2. Calculating the area:
The area of the part of the circle above the line can be calculated by finding the area of the sector formed by the two intersection points and subtracting the area of the triangle formed by the two intersection points and the origin (0,0).

- Area of the sector:
The angle formed by the two intersection points and the origin is the angle at the center of the circle. This angle can be calculated using trigonometry:
θ = 2 * arctan(y/x)
For x = 1.632 and y = 3.264:
θ = 2 * arctan(3.264/1.632)
θ ≈ 2.312 radians

The area of the sector is given by:
A_sector = (θ/2π) * πr^2
where r is the radius of the circle.

Since the equation of the circle is x^2 + y^2 - 2x - 4y - 1 = 0, we can complete the square to find the radius:
(x^2 - 2x + 1) + (y^2 - 4y + 4) = 6
(x - 1)^2 + (y - 2)^2 = 6

Comparing this to the standard equation of a circle (x - h)^2 + (y - k)^

The area bounded by the parabolas y = 5x2and y − 9 = 2x2 is
  • a)
    12√3 sq.units
  • b)
    6√2 sq.units
  • c)
    12√2 sq.units
  • d)
    4√3 sq.units
Correct answer is option 'A'. Can you explain this answer?

Explanation:

Finding the Points of Intersection:
To find the points of intersection of the two parabolas, set them equal to each other:
5x^2 = 9 - 2x^2
7x^2 = 9
x^2 = 9/7
x = ±√(9/7)

Calculating the Area Between the Curves:
Integrate the difference of the two equations between the points of intersection to find the area:
∫(9 - 2x^2) - 5x^2 dx from -√(9/7) to √(9/7)
= ∫(9 - 7x^2) dx from -√(9/7) to √(9/7)
= [9x - (7x^3)/3] from -√(9/7) to √(9/7)

Substitute the Values:
= [9√(9/7) - (7(9/7)^(3/2))/3] - [-9√(9/7) - (7(9/7)^(3/2))/3]
= (27/√7 - 21√7/3) - (-27/√7 - 21√7/3)
= 54/√7

Final Calculation:
To find the area, square the result:
(54/√7)^2 = 2916/7 = 123 sq. units
Therefore, the area bounded by the parabolas y = 5x^2 and y = 9 - 2x^2 is 123 sq. units.

Let y be the function which passes through (1 , 2) having slope (2x + 1) . The area bounded between the curve and the x – axis is
  • a)
    1/6 sq. units
  • b)
    6 sq. units
  • c)
    5/6 sq. units
  • d)
    none of these
Correct answer is option 'A'. Can you explain this answer?

Rhea Joshi answered
Given slope of the curve is 2x + 1.

Also , it passes through (1, 2).
∴ 2 = 1+1+c ⇒ c = 0
Equation of curve is : y = x2 + x. Therefore , points of intersection of y = x (x +1) and the x – axis are x = 0 , x = - 1.
Required area :

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