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JEE Main 20154 April
Exam
JEE Main
Year
2015
Date
4 April
Subject
Mathematics
Chapter
Area Under Curves

JEE Main 2015 · 4 April · Mathematics · Area Under Curves

The area (in sq. units) of the region described by [ (x, y) : y ^ 2...

The area (in sq. units) of the region described by \left[\left(x, y\right): {y}^{2} \le 2xandy \ge 4x - 1\right] isThe area (in sq. units) of the region described by [ (x, y) : y ^ 2 ≤ 2xandy ≥ 4x - 1] is

Options

  1. A932sq.units\dfrac{9}{32}sq . units
  2. B732sq.units\dfrac{7}{32}sq . units
  3. C564sq.units\dfrac{5}{64}sq . units
  4. D1564sq.units\dfrac{15}{64}sq . units

Correct answer

A. 932sq.units\dfrac{9}{32}sq . units

Step-by-step solution

The area (in sq. units) of the region described by [ (x, y) : y ^ 2 ≤ 2xandy ≥ 4x - 1] is

Let us find the points intersections of y2=2x{y}^{2} = 2x and y=4x−1y = 4x - 1

⇒(4x−1)2=2x⇒ {\left(4x - 1\right)}^{2} = 2x

⇒16x2−10x+1=0⇒ 16{x}^{2} - 10x + 1 = 0

⇒(8x−1)(2x−1)=0⇒ \left(8x - 1\right)\left(2x - 1\right) = 0

⇒x=12,18⇒x = \dfrac{1}{2}, \dfrac{1}{8}

x=12⇒y=4(12)−1=1⇒A(12,1)x = \dfrac{1}{2} ⇒ y = 4\left(\dfrac{1}{2}\right) - 1 = 1 ⇒ A\left(\dfrac{1}{2}, 1\right)

x=18⇒y=4(18)−1=−12⇒B(18,−12)x = \dfrac{1}{8} ⇒ y = 4\left(\dfrac{1}{8}\right) - 1 = \dfrac{- 1}{2} ⇒ B\left(\dfrac{1}{8}, \dfrac{- 1}{2}\right)

A1=∫0182xdx+12×18×12{A}_{1} = {∫}_{0}^{\dfrac{1}{8}}\sqrt{2x}dx + \dfrac{1}{2} \times \dfrac{1}{8} \times \dfrac{1}{2}

A1=2[x3232]018+132{A}_{1} = \sqrt{2}{\left[\dfrac{{x}^{\dfrac{3}{2}}}{\dfrac{3}{2}}\right]}_{0}^{\dfrac{1}{8}} + \dfrac{1}{32}

A1=124+132sq.units{A}_{1} = \dfrac{1}{24} + \dfrac{1}{32}sq . units

A2=∫0122xdx−12×1×14{A}_{2} = {∫}_{0}^{\dfrac{1}{2}}\sqrt{2x}dx - \dfrac{1}{2} \times 1 \times \dfrac{1}{4}

A2=2[x3232]012−18{A}_{2} = \sqrt{2}{\left[\dfrac{{x}^{\dfrac{3}{2}}}{\dfrac{3}{2}}\right]}_{0}^{\dfrac{1}{2}} - \dfrac{1}{8}

A2=524sq.units{A}_{2} = \dfrac{5}{24}sq . units

Therefore, the required area is,

A=124+132+524=932sq.unitsA = \dfrac{1}{24} + \dfrac{1}{32} + \dfrac{5}{24} = \dfrac{9}{32}sq . units

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