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 (x–2)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]
= 32−23 = 56
Area OACO = ∫−10x+24 dx - ∫−10x24 dx
= 14|x2+2+2x|−10| - 14|x33|−10
= 14|−122−2−1| - 14|−(−13)3|
= 14|−12+2| - 14(13)
= 38−112 = 724
Therefore, required area = (56+724) = 98 sq. units
OR
Given equations of the circles are
x2+y2 = 4 ... (1)
(x−2)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:
(x−2)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−(x−2)2 dx + ∫124−x2 dx]
= 2
[12(x−2)4−(x−2)2+4sin−1(x−22)]01
+ [x4−x2+4sin−1x2]12
=
[(−3+4sin−1(−12))−4sin−1(−1)]
+ [4sin−11−3−4sin−112]
= [(−3−4×π6)+4×π2] + [4×π2−3−4×π6]
= 8π3 - 2 3
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