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Area Under the Curves question

2022 · 26 Jun · Shift 2 · Q30
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  5. /2022 · 26 Jun · Shift 2 · Q30

Area Under the Curves question

2022 · 26 Jun · Shift 2 · Q30

JEE MainMathematicsArea Under the CurvesMCQ+4 / −1
The area of the region bounded by y2 = 8x and y2 = 16(3 −-− x) is equal to:
  1. A
    323{{32} \over 3}332​
  2. B
    403{{40} \over 3}340​
  3. C
    16
  4. D
    19
View written solutionFree

Correct answer: C

  1. Interpret the curves

The given equations are:

y2=8xy^2 = 8xy2=8x y2=16(3−x)y^2 = 16(3-x)y2=16(3−x)

Rewrite the second one:

y2=48−16xy^2 = 48 - 16xy2=48−16x

or

x=3−y216x = 3 - \frac{y^2}{16}x=3−16y2​

From the first curve,

x=y28x = \frac{y^2}{8}x=8y2​

So for a given yyy, the region is between:

  • left curve: x=y28x = \frac{y^2}{8}x=8y2​
  • right curve: x=3−y216x = 3 - \frac{y^2}{16}x=3−16y2​

  1. Find points of intersection

At intersection,

y28=3−y216\frac{y^2}{8} = 3 - \frac{y^2}{16}8y2​=3−16y2​

Multiply by 161616:

2y2=48−y22y^2 = 48 - y^22y2=48−y2

3y2=483y^2 = 483y2=48

y2=16y^2 = 16y2=16

y=±4y = \pm 4y=±4

Now find xxx:

x=y28=168=2x = \frac{y^2}{8} = \frac{16}{8} = 2x=8y2​=816​=2

So the curves intersect at (2,4)(2,4)(2,4) and (2,−4)(2,-4)(2,−4).


  1. Set up the area integral

Area between curves using horizontal strips:

A=∫−44[(3−y216)−(y28)]dyA = \int_{-4}^{4} \left[\left(3 - \frac{y^2}{16}\right) - \left(\frac{y^2}{8}\right)\right] dyA=∫−44​[(3−16y2​)−(8y2​)]dy

Simplify:

A=∫−44(3−y216−y28)dyA = \int_{-4}^{4} \left(3 - \frac{y^2}{16} - \frac{y^2}{8}\right) dyA=∫−44​(3−16y2​−8y2​)dy

A=∫−44(3−3y216)dyA = \int_{-4}^{4} \left(3 - \frac{3y^2}{16}\right) dyA=∫−44​(3−163y2​)dy


  1. Evaluate the integral

Since the integrand is even,

A=2∫04(3−3y216)dyA = 2\int_{0}^{4} \left(3 - \frac{3y^2}{16}\right) dyA=2∫04​(3−163y2​)dy

A=2[3y−316⋅y33]04A = 2\left[3y - \frac{3}{16}\cdot \frac{y^3}{3}\right]_0^4A=2[3y−163​⋅3y3​]04​

A=2[3y−y316]04A = 2\left[3y - \frac{y^3}{16}\right]_0^4A=2[3y−16y3​]04​

At y=4y=4y=4:

3(4)−4316=12−6416=12−4=83(4) - \frac{4^3}{16} = 12 - \frac{64}{16} = 12 - 4 = 83(4)−1643​=12−1664​=12−4=8

So,

A=2(8)=16A = 2(8) = 16A=2(8)=16


  1. Compare with options

The area is

16\boxed{16}16​

So the correct option is C.


  1. Comparison with stored correct answer

Stored correct answer: C

Derived answer: C

They match.

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