Medium MCQ +4 / -1 PYQ · JEE Mains 2022

A particle is moving in the xy-plane along a curve C passing through the point (3, 3). The tangent to the curve C at the point P meets the x-axis at Q. If the y-axis bisects the segment PQ, then C is a parabola with :

  1. A length of latus rectum 3 Correct answer
  2. B length of latus rectum 6
  3. C focus $\left( {{4 \over 3},0} \right)$
  4. D focus $\left( {0,{3 \over 4}} \right)$

Solution

<p>According to the question (Let P(x, y))</p> <p>$2x - y{{dx} \over {dy}} = 0$</p> <p>($\because$ equation of tangent at $P:y - y = {{dy} \over {dx}}(y - x)$)</p> <p>$\therefore$ $2{{dy} \over {y}} = {{dx} \over x}$</p> <p>$\Rightarrow 2\ln y = \ln x + \ln c$</p> <p>$\Rightarrow {y^2} = cx$</p> <p>$\because$ this curve passes through (3, 3)</p> <p>$\therefore$ c = 3</p> <p>$\therefore$ required parabola ${y^2} = 3x$ and L.R = 3</p>

About this question

Subject: Mathematics · Chapter: Conic Sections · Topic: Parabola

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