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JEE Main 20203 SeptemberMorning Shift
Exam
JEE Main
Year
2020
Date
3 September
Shift
Morning Shift
Subject
Mathematics
Chapter
Parabola

JEE Main 2020 · 3 September · Morning Shift · Mathematics · Parabola

Let P be a point on the parabola, y ^ 2 = 12x and N be the foot of...

Let PP be a point on the parabola, y2=12x{y}^{2} = 12x and NN be the foot of the perpendicular drawn from PP , on the axis of the parabola. A line is now drawn through the mid-point MM of PNPN, parallel to its axis which meets the parabola at QQ. If the y−y -intercept of the line NQNQ is 43,\dfrac{4}{3}, then :Let P be a point on the parabola, y ^ 2 = 12x and N be the foot of the perpendicular drawn from P , on the axis of the

Options

  1. APN=4PN = 4
  2. BMQ=13MQ = \dfrac{1}{3}
  3. CMQ=14MQ = \dfrac{1}{4}
  4. DPN=3PN = 3

Correct answer

C. MQ=14MQ = \dfrac{1}{4}

Step-by-step solution

Comparing the equation of the parabola, with standard equation y2=4ax{y}^{2} = 4ax, we get a=3a = 3.

Figure is drawn on the basis of the given information.

Let P be a point on the parabola, y ^ 2 = 12x and N be the foot of the perpendicular drawn from P , on the axis of the

Parametric form of parabola is x=at2,y=2atx = a{t}^{2}, y = 2at

∴P=(3t2,6t)∴ P = \left(3{t}^{2}, 6t\right), N=(3t2,0)N = \left(3{t}^{2}, 0\right), M=(3t2,3t)M = \left(3{t}^{2}, 3t\right)

⇒Q=(3t24,3t)⇒ Q = \left(\dfrac{3{t}^{2}}{4}, 3t\right)

Equation of NQNQ: y−0=(3t−03t24−3t2)(x−3t2)y - 0 = \left(\dfrac{3t - 0}{\dfrac{3{t}^{2}}{4} - 3{t}^{2}}\right)\left(x - 3{t}^{2}\right)

i.e., y=−43t⋅(x−3t2)⇒y=−43t⋅x+4ty = \dfrac{- 4}{3t} \cdot \left(x - 3{t}^{2}\right) ⇒ y = \dfrac{- 4}{3t} \cdot x + 4t

⇒4t=43⇒t=13⇒ 4t = \dfrac{4}{3} ⇒ t = \dfrac{1}{3}

PN=6t=2PN = 6t = 2

MQ=3t2−3t24=9t24=14MQ = 3{t}^{2} - \dfrac{3{t}^{2}}{4} = \dfrac{9{t}^{2}}{4} = \dfrac{1}{4}

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