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JEE Main 202120 JulyMorning Shift
Exam
JEE Main
Year
2021
Date
20 July
Shift
Morning Shift
Subject
Mathematics
Chapter
Parabola

JEE Main 2021 · 20 July · Morning Shift · Mathematics · Parabola

Let the tangent to the parabola S: y ^ 2 = 2x at the point P(2, 2)...

Let the tangent to the parabola S:y2=2xS: {y}^{2} = 2x at the point $P(2,2)P\left(2, 2\right) meet the x−x -axis at QandnormalatitmeettheparabolaQ and normal at it meet the parabolaSatthepointat the pointR.Thenthearea(insq.units)ofthetriangle. Then the area (in sq. units) of the trianglePQR$ is equal to:Let the tangent to the parabola S: y ^ 2 = 2x at the point P(2, 2) meet the x - axis at Q and normal at it meet the

Options

  1. A252\dfrac{25}{2}
  2. B352\dfrac{35}{2}
  3. C152\dfrac{15}{2}
  4. D2525

Correct answer

A. 252\dfrac{25}{2}

Step-by-step solution

We have,

y2=2x{y}^{2} = 2x

Let the tangent to the parabola S: y ^ 2 = 2x at the point P(2, 2) meet the x - axis at Q and normal at it meet the

Tangent at $P(2,2)P\left(2, 2\right) is

y(2)=2(12)(x+2)y\left(2\right) = 2\left(\dfrac{1}{2}\right)\left(x + 2\right)

⇒2y=x+2⇒ 2y = x + 2

It meets x−x -axis at y=0y = 0 i.e., x=−2x = - 2

∴Q≡(−2,0)∴ Q ≡ \left(- 2, 0\right)

Normal at PP is

⇒y−2=−2(x−2)⇒ y - 2 = - 2\left(x - 2\right)

⇒y=6−2x⇒ y = 6 - 2x

∴∴ Solving with y2=2x{y}^{2} = 2x, we get

(6−2x)2=2x{\left(6 - 2x\right)}^{2} = 2x

⇒4x2+36−24x=2x⇒ 4{x}^{2} + 36 - 24x = 2x

⇒4x2−26x+36=0⇒ 4{x}^{2} - 26x + 36 = 0

⇒2x2−13x+18=0⇒ 2{x}^{2} - 13x + 18 = 0

⇒x=13±169−1444=13±54⇒ x = \dfrac{13 \pm \sqrt{169 - 144}}{4} = \dfrac{13 \pm 5}{4}

⇒x=92,12⇒ x = \dfrac{9}{2}, \dfrac{1}{2}

∴R≡(92,−3)∴ R ≡ \left(\dfrac{9}{2}, - 3\right)

∴ Ar\left(\delta PQR\right) = \dfrac{1}{2}\left|\begin{cases}2 & 2 & 1 \\ - 2 & 0 & 1 \\ \dfrac{9}{2} & - 3 & 1\end{cases}\right|

⇒Ar(δPQR)=12[2⋅3−2(−2−92)+6]⇒ Ar\left(\delta PQR\right) = \dfrac{1}{2}\left[2 \cdot 3 - 2\left(- 2 - \dfrac{9}{2}\right) + 6\right]

⇒Ar(δPQR)=12[12+13]⇒ Ar\left(\delta PQR\right) = \dfrac{1}{2}\left[12 + 13\right]
$⇒ Ar\left(\delta PQR\right) = \dfrac{25}{2} sq.units

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