CBSE Class 12 Math 2013 Solved Paper

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Question : 25 of 29
 
Marks: +1, -0
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 (1,14). Co-ordinates of point B are (2, 1).
Area OBAO = Area OBCO + Area OACO … (1)
Area OBCO = 02x+24 dx - 02x24 dx
= 14[x22+2x]02 - 14[x33]02
= 12 (2 + 4) - 14[83]
= 3223 = 56
Area OACO = 10x+24 dx - 10x24 dx
= 14|x2+2+2x|10| - 14|x33|10
= 14|12221| - 14|(13)3|
= 14|12+2| - 14(13)
= 38112 = 724
Therefore, required area = (56+724) = 98 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 [01ydx+12ydx]
= 2 [014(x2)2 dx + 124x2 dx]
= 2
[12(x2)4(x2)2+4sin1(x22)]01
+ [x4x2+4sin1x2]12
=
[(3+4sin1(12))4sin1(1)]
+ [4sin1134sin112]
= [(34×π6)+4×π2] + [4×π234×π6]
= 8π3 - 2 3
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