CBSE Class 12 Math 2008 Solved Paper

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Question : 25
Total: 29
Using integration find the area of the region bounded by the parabola y2 = 4x and the circle 4x2+4y2 = 9.
Solution:  
The respective equations for the parabola and the circle are:
y2 = 4x ... (1)
4x2+4y2 = 9 ... (2)
or x2+y2 = (
3
2
)
2

Equation (1) is a parabola with vertex (0, 0) which opens to the right and equation (2) is a circle with centre (0, 0) and radius
3
2

From equations (1) and (2), we get:
4x2 + 4 (4x) = 9
4x2 + 16x - 9 = 0
4x2 + 18x - 2x - 9 = 0
2x (2x + 9) - 1 (2x + 9) = 0
(2x + 9) (2x - 1) = 0
x = -
9
2
,
1
2

For x = −
9
2
, y2 = 4 (−
9
2
)
, which is not possible, hence x =
1
2

Therefore, the given curves intersect at x =
1
2


Required area of the region bound by the two curves
= 2
1
2
∫
0
2√xdx
+ 2‌
3
2
∫
1
2
√
9
4
−x2
d
x

= 4 |
2
3
x
3
2
|
0
1
2
+ 2
|
x
2
√
9
4
−x2
+
9
8
s
i
n−1
(
2x
3
)
s
i
n−1
(
2x
3
)
|
1
2
3
2

=
8
3
(
1
8
)
1
2
+ 2
|0+
9
8
s
i
n−1
−
1
4
√2
−
9
8
s
i
n−1
(
1
3
)
|

=
8
3
(
1
2√2
)
+
9
4
(
Ï€
2
)
-
√2
2
−
9
4
s
i
n−1
(
1
3
)

=
2√2
3
+
9Ï€
8
-
√2
2
−
9
4
s
i
n−1
(
1
3
)
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