NCERT Solutions for Class 12 Maths Exercise 8.1 Chapter 8 Application of Integrals – FREE PDF Download
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NCERT Solutions for Class 12 Maths Chapter 8 Application of Integrals (Ex 8.1) Exercise 8.1
1. Find the area of the region bounded by the curve and the lines and the axis.
……….(i)
Required area (shaded region)
= [From eq. (i)]
= = =
= = = sq. units
2. Find the area of the region bounded by and the axis in the first quadrant.
……….(i)
Required area (shaded region) bounded by curve (vertical lines ) and axis in first quadrant.
= ∣∣∣∫24ydx∣∣∣=∣∣∣∫243x−−√dx∣∣∣|∫24ydx|=|∫243xdx| [From eq. (i)]
= =
= =
= = sq. units
3. Find the area of the region bounded by and the axis in the first quadrant.
Required (shaded) area bounded by curve (Horizontal lines ) and axis in first quadrant.
=
= = = sq. units
4. Find the area of the region bounded by the ellipse
Here
From eq. (i),
y=±3416−x2−−−−−−√y=±3416−x2……….(ii)
For arc of ellipse in first quadrant.
Ellipse (i) ia symmetrical about axis,
( On changing in eq. (i), it remains unchanged)
Ellipse (i) ia symmetrical about axis,
( On changing in eq. (i), it remains unchanged)
Intersections of ellipse (i) with axis
Putting in eq. (i),
Therefore, Intersections of ellipse (i) with axis are (0, 4) and .
Intersections of ellipse (i) with axis
Putting in eq. (i),
Therefore, Intersections of ellipse (i) with axis are (0, 3) and .
Now Area of region bounded by ellipse (i) = Total shaded area
= 4 x Area OAB of ellipse in first quadrant
= [ At end B of arc AB of ellipse; and at end A of arc AB ; ]
= =
=
= =
= sq. units
5. Find the area of the region bounded by the ellipse
Here
From eq. (i),
y=±324−x2−−−−−√y=±324−x2……….(ii)
for arc of ellipse in first quadrant.
Ellipse (i) ia symmetrical about axis,
( On changing in eq. (i), it remains unchanged)
Ellipse (i) ia symmetrical about axis,
( On changing in eq. (i), it remains unchanged)
Intersections of ellipse (i) with axis
Putting in eq. (i),
Therefore, Intersections of ellipse (i) with axis are (0, 2) and .
Intersections of ellipse (i) with axis
Putting in eq. (i),
Therefore, Intersections of ellipse (i) with axis are (0, 3) and .
Now Area of region bounded by ellipse (i) = Total shaded area
= 4 x Area OAB of ellipse in first quadrant
= [ At end B of arc AB of ellipse; and at end A of arc AB ; ]
= =
=
=
= sq. units
6. Find the area of the region in the first quadrant enclosed by axis, line and the circle
Equation of the circle is ……….(i)
We know that eq. (i) represents a circle whose centre is (0, 0) and radius is 2.
Equation of the given line is
……….(ii)
We know that eq. (ii) being of the form where represents a straight line passing through the origin and making angle of with axis.
Step II. To find values of and Putting from eq. (ii) in eq. (i),
Putting in , and
Therefore, the two points of intersections of circle (i) and line (ii) are A and D.
Step III. Now shaded area OAM between segment OA of line (ii) and axis
=
= = = = = sq. units……….(iii)
Step IV. Now shaded area AMB between are AB of circle and axis.
= =
= From eq. (ii),
= =
= = = sq. units……….(iv)
Step V. Required shaded area OAB = Area of OAM + Area of AMB
= sq. units
7. Find the area of the smaller part of the circle cut off by the line
……….(ii)
Here Area of smaller part of the circle cut off by the line = Area of ABMC = 2 x Area of ABM
= = [From eq. (ii)]
=
=
= 2[0+a22.π2−a2√×a2√−a22sin−112√]2[0+a22.π2−a2×a2−a22sin−112]
= 2[πa24−a2√×a2√−a22.π4]2[πa24−a2×a2−a22.π4]
= 2[πa24−a22−πa28]2[πa24−a22−πa28]
= 2a2[π4−12−π8]2a2[π4−12−π8]
= 2a2[2π−2−π8]2a2[2π−2−π8]
= a24(π−2)=πa24−a22a24(π−2)=πa24−a22
=>a22(π2−1)=>a22(π2−1)sq. units
8. The area between and is divided into two equal parts by the line find the value of
Now area bounded by parabola (i) and vertical line is divided into two equal parts by the vertical line
Area OAMB = Area AMBDNC
=
=
=
units
9. Find the area of the region bounded by the parabola and
To find: Area between the parabola and the ray for
Here, Limits of integration
Now, for , table of values,
if if
0 | 1 | 2 | |
0 | 1 | 2 |
0 | |||
0 | 1 | 2 |
Now, Area between parabola and axis between limits and
= = = ………..(i)
And Area of ray and axis,
= = = ………..(ii)
Required shaded area in first quadrant = Area between ray for and axis Area between parabola and axis in first quadrant
= Area given by eq. (ii) – Area given by eq. (i) = sq. units
Similarly, shaded area in second quadrant = 1616sq. units
Therefore, total area of shaded region in the above figure = 1616+ 1616= 1313sq. units
10. Find the area bounded by the curve x2=4yx2=4y and the line
Equation of the given curve is
……..(i)
Equation of the given line is
……….(ii)
0 | 1 | ||
0 | 0 |
Step II. Putting from eq. (i) in eq. (ii),
x(x−2)+1(x−2)=0x(x−2)+1(x−2)=0
or
For ,from eq. (i), (2, 1)
For from eq. (i),
Therefore, the two points of intersection of parabola (i) and line (ii) are C and D (2, 1).
Step III. Area CMOEDN between parabola (i) and axis = =
= = = sq. units……..(iii)
Step IV. Area of trapezium CMND between line (ii) and axis = =
= = = =
= = sq. units……….(iv)
Required shaded area = Area given by eq. (iv) – Area given by eq. (iii)
= sq. units
11. Find the area of the region bounded by the curve and the line
………(i)
y=2x−−√y=2x ………(ii)
Here required shaded area OAMB = 2 x Area OAM
= = =
= = = sq. units
12. Choose the correct answer:
Area lying in the first quadrant and bounded by the circle and the lines and is
(A)
(B)
(C)
(D)
……….(ii)
Required area = =
=
=
= = sq. units
Therefore, option (A) is correct.
13. Choose the correct answer:
Area of the region bounded by the curve axis and the line is:
(A) 2
(B)
(C)
(D)
Required area = Area OAM = = ∣∣∣∫03y24dy∣∣∣|∫03y24dy|
= 14∣∣∣(y33)30∣∣∣14|(y33)03| = sq. units
Therefore, option (B) is correct.