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

The equation of a common tangent to the parabolas $y=x^{2}$ and $y=-(x-2)^{2}$ is

  1. A $y=4(x-2)$
  2. B $y=4(x-1)$ Correct answer
  3. C $y=4(x+1)$
  4. D $y=4(x+2)$

Solution

<p>Equation of tangent of slope $m$ to $y$ $= x^2$</p> <p>$y = mx - {1 \over 4}{m^2}$</p> <p>Equation of tangent of slope $m$ to $y = - {(x - 2)^2}$</p> <p>$y = m(x - 2) + {1 \over 4}{m^2}$</p> <p>If both equation represent the same line</p> <p>${1 \over 4}{m^2} - 2m = - {1 \over 4}{m^2}$</p> <p>$m = 0,\,4$</p> <p>So, equation of tangent</p> <p>$y = 4x - 4$</p>

About this question

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

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