Q42 / 90 · JEE Main 2023 (30 Jan Shift 1) · Mathematics

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

  • A
    2
  • B
    4
  • C
    8
  • Correct answer
    D
    6

Solution

Given parabola is

x=4y2

⇒y2=14x

⇒y2=4×116×x

Equation of normal is

y=-tx+2at+at3

⇒y=-tx+216t+116t3

It passes through Q0,33, so

33=t8+t316

⇒t3+2t-528=0

⇒t-8t2+8t+66=0

⇒t=8

So,

P≡h,k≡at2,2at≡(4,1)

Now, we have parabola 

y2=4x+y

⇒y2-4y=4x

⇒y-22=4x+1

Equation of directrix is

x+1=-1

⇒x=-2

So, distance of point 4,1 from the line x+2=0 is

=4+21=6 units

Hence, the correct answer is option: 'D'.

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