RD Sharma - Mathematics (Volume 2)

Book: RD Sharma - Mathematics (Volume 2)

Chapter: 21. Areas of Bounded Regions

Subject: Maths - Class 12th

Q. No. 21 of Exercise 21.3

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21

Find the area enclosed by the parabolas y = 5x2 and y = 2x2 + 9.

To find the area enclosed by

y = 5x2 ...(i)


and y = 2x2 + 9 ...(ii)


On solving the equation (i) and (ii),


5x2 = 2x2 + 9


Or 3x2 = 9


Or x =


Or 15


Equation (i) represents a parabola with vertex O (0, 0) and axis as y - axis .


Equation (ii) represents a parabola with vertex C (0, 9) and axis as the y - axis.


Points of intersection of parabolas are A (√3, 15) and B( – √3,15)


These are shown in the graph below: -



Required area = Region AOBCA


= 2(Region AOCA)







The area enclosed by the parabolas y = 5x2 and y = 2x2 + 9 is


21

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