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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 

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 curve y = x[x], the x – axis and the ordinates x = 1 and x = -1 is given by
  • a)
    0
  • b)
    1/2
  • c)
    2/3
  • d)
    none of these
Correct answer is option 'B'. Can you explain this answer?

Shruti Sharma answered
Understanding the Problem
To find the area bounded by the curve y = x[x], the x-axis, and the vertical lines x = -1 and x = 1, we first need to determine the behavior of the function y = x[x].
Analyzing the Function
- The function y = x[x] involves the greatest integer function [x], which takes the largest integer less than or equal to x.
- For x in the interval [-1, 0), [x] = -1, resulting in y = x * (-1) = -x.
- For x in the interval [0, 1), [x] = 0, resulting in y = x * 0 = 0.
This means we can break the area calculation into two parts:
Calculating Areas
1. For x in [-1, 0):
- The function simplifies to y = -x.
- The area under this curve from x = -1 to x = 0 is given by the integral:
Area = ∫[-1 to 0] (-x) dx = [-(x^2)/2] from -1 to 0 = [0 - (-1/2)] = 1/2.
2. For x in [0, 1):
- The function simplifies to y = 0.
- The area under this curve from x = 0 to x = 1 is 0.
Total Area Calculation
- The total area bounded by the curve, the x-axis, and the ordinates is simply the area calculated from the interval [-1, 0], which is:
Total Area = Area from [-1, 0] + Area from [0, 1] = 1/2 + 0 = 1/2.
Conclusion
Thus, the area bounded by the curve y = x[x], the x-axis, and the ordinates x = -1 and x = 1 is indeed 1/2, confirming that the correct answer is option 'B'.

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 :

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 curves y2 = 4x and y = x is equal to
  • a)
    8/3
  • b)
    35/6
  • c)
    1/3
  • d)
    none of these
Correct answer is option 'A'. Can you explain this answer?

Pranav Pillai answered
The two curves y2 = 4x and y = x meet where x2 = 4x i.e ..where x = 0 or x = 4 . Moreover , the parabola lies above the line y = x between x = 0 and x = 4 . Hence , the required are 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.

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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