CBSE Class 12 Math 2013 Solved Paper

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Question : 25
Total: 29
Using integration, find the area bounded by the curve x2 = 4y and the line x = 4y – 2.
OR
Using integration, find the area of the region enclosed between the two circles
x2+y2 = 4 and (x2)2+y2 = 4.
Solution:  
The shaded area OBAO represents the area bounded by the curve x2 = 4y and line x = 4y – 2.

Let A and B be the points of intersection of the line and parabola.
Co-ordinates of point A are (1,
1
4
)
. Co-ordinates of point B are (2, 1).
Area OBAO = Area OBCO + Area OACO … (1)
Area OBCO =
2
0
x+2
4
dx -
2
0
x2
4
dx
=
1
4
[
x2
2
+2x
]
02
-
1
4
[
x3
3
]
02

=
1
2
(2 + 4) -
1
4
[
8
3
]

=
3
2
2
3
=
5
6

Area OACO =
0
1
x+2
4
dx -
0
1
x2
4
dx
=
1
4
|x2+2+2x
|10
|
-
1
4
|
x3
3
|10

=
1
4
|
12
2
2
1
|
-
1
4
|(
1
3
)
3
|

=
1
4
|
1
2
+2
|
-
1
4
(
1
3
)

=
3
8
1
12
=
7
24

Therefore, required area = (
5
6
+
7
24
)
=
9
8
sq. units
OR
Given equations of the circles are
x2+y2 = 4 ... (1)
(x2)2+y2 = 4 ... (2)
Equation (1) is a circle with centre O at the origin and radius 2. Equation (2) is a circle with centre C (2, 0) and radius 2.
Solving (1) and (2), we have:
(x2)2+y2 = x1+y2
x2 - 4x + 4 + y2 = x2+y2
x = 1
This gives y = ±3
Thus, the points of intersection of the given circles are A (1 , 3) and A' (1 , - 3) as shown in the figure.

Required area
= Area of the region OACA'O
= 2 [area of the region ODCAO]
= 2 [area of the region ODAO + area of the region DCAD]
= 2 [
1
0
ydx
+
2
1
ydx
]

= 2 [
1
0
4(x2)2
dx +
2
1
4x2
dx]
= 2
[
1
2
(x2)
4(x2)2
+4sin1(
x2
2
)
]
01
+ [x4x2+4sin1
x
2
]
12

=
[(3+4sin1(
1
2
)
)
4sin1(1)
]
+ [4sin1134sin1
1
2
]

= [(34×
π
6
)
+4×
π
2
]
+ [4×
π
2
3
4×
π
6
]

=
8π
3
- 2 3
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