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Question : 25
Total: 29
Using integration, find the area bounded by the curve x 2 = 4y and the line x = 4y – 2.
OR
Using integration, find the area of the region enclosed between the two circles
x 2 + y 2 = 4 and ( x – 2 ) 2 + y 2 = 4.
OR
Using integration, find the area of the region enclosed between the two circles
Solution:
The shaded area OBAO represents the area bounded by the curve x 2 = 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 ,
) . Co-ordinates of point B are (2, 1).
Area OBAO = Area OBCO + Area OACO … (1)
Area OBCO =
dx -
dx
=
[
+ 2 x ] 0 2 -
[
] 0 2
=
(2 + 4) -
[
]
=
−
=
Area OACO =
dx -
dx
=
| x 2 + 2 + 2 x | − 1 0 | -
|
| − 1 0
=
|
− 2 − 1 | -
| − ( −
) 3 |
=
| −
+ 2 | -
(
)
=
−
=
Therefore, required area =(
+
) =
sq. units
OR
Given equations of the circles are
x 2 + y 2 = 4 ... (1)
( x − 2 ) 2 + y 2 = 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:
( x − 2 ) 2 + y 2 = x 1 + y 2
x 2 - 4x + 4 + y 2 = x 2 + y 2
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[
y d x +
y d x ]
= 2 [
√ 4 − ( x − 2 ) 2 dx +
√ 4 − x 2 dx]
= 2[
( x − 2 ) √ 4 − ( x − 2 ) 2 + 4 s i n − 1 (
) ] 0 1 + [ x √ 4 − x 2 + 4 s i n − 1
] 1 2
=[ ( − √ 3 + 4 s i n − 1 (
) ) − 4 s i n − 1 ( − 1 ) ] + [ 4 s i n − 1 1 − √ 3 − 4 s i n − 1
]
=[ ( − √ 3 − 4 ×
) + 4 ×
] + [ 4 ×
− √ 3 − 4 ×
]
=
- 2 √ 3
Let A and B be the points of intersection of the line and parabola.
Co-ordinates of point A are
Area OBAO = Area OBCO + Area OACO … (1)
Area OBCO =
=
=
=
Area OACO =
=
=
=
=
Therefore, required area =
OR
Given equations of the circles are
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:
x = 1
This gives y =
Thus, the points of intersection of the given circles are A (1 ,
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
= 2 [
= 2
=
=
=
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