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JEE Main 202330 JanuaryMorning Shift
Exam
JEE Main
Year
2023
Date
30 January
Shift
Morning Shift
Subject
Mathematics
Chapter
Parabola

JEE Main 2023 · 30 January · Morning Shift · Mathematics · Parabola

If P ( h, k ) be point on the parabola x = 4 y ^ 2 , which is...

If P(h,k)P ( h, k ) be point on the parabola x=4y2x = 4{y}^{2}, which is nearest to the point Q(0,33)Q ( 0, 33 ), then the distance of PP from the directrix of the parabola y2=4(x+y){y}^{2} = 4 ( x + y ) is equal to:

Options

  1. A22
  2. B44
  3. C88
  4. D66

Correct answer

D. 66

Step-by-step solution

Given parabola is

x=4y2x = 4{y}^{2}

⇒y2=14x⇒ {y}^{2} = \dfrac{1}{4}x

⇒y2=4×116×x⇒ {y}^{2} = 4 \times \dfrac{1}{16} \times x

Equation of normal is

y=−tx+2at+at3y = - tx + 2at + a{t}^{3}

⇒y=−tx+216t+116t3⇒ y = - tx + \dfrac{2}{16}t + \dfrac{1}{16}{t}^{3}

It passes through Q(0,33)Q\left(0, 33\right), so

33=t8+t31633 = \dfrac{t}{8} + \dfrac{{t}^{3}}{16}

⇒t3+2t−528=0⇒ {t}^{3} + 2t - 528 = 0

⇒(t−8)(t2+8t+66)=0⇒ \left(t - 8\right)\left({t}^{2} + 8t + 66\right) = 0

⇒t=8⇒ t = 8

So,

P≡(h,k)≡(at2,2at)≡(4,1)P ≡ \left(h, k\right) ≡ \left(a{t}^{2}, 2at\right) ≡ ( 4, 1 )

Now, we have parabola

y2=4(x+y){y}^{2} = 4\left(x + y\right)

⇒y2−4y=4x⇒ {y}^{2} - 4y = 4x

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

Equation of directrix is

x+1=−1x + 1 = - 1

⇒x=−2⇒ x = - 2

So, distance of point \left(4, 1\right)fromthelinefrom the linex + 2 = 0is</p><p>is</p><p>= \left|\dfrac{4 + 2}{1}\right| = 6$ units

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