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JEE Main 202124 FebruaryEvening Shift
Exam
JEE Main
Year
2021
Date
24 February
Shift
Evening Shift
Subject
Mathematics
Chapter
Parabola

JEE Main 2021 · 24 February · Evening Shift · Mathematics · Parabola

If P is a point on the parabola y = x ^ 2 + 4 which is closest to...

If PP is a point on the parabola y=x2+4y = {x}^{2} + 4 which is closest to the straight line y=4x−1,y = 4x - 1, then the co-ordinates of PP are:If P is a point on the parabola y = x ^ 2 + 4 which is closest to the straight line y = 4x - 1, then the co-ordinates

Options

  1. A(−2,8)\left(- 2, 8\right)
  2. B(1,5)\left(1, 5\right)
  3. C(2,8)\left(2, 8\right)
  4. D(3,13)\left(3, 13\right)

Correct answer

C. (2,8)\left(2, 8\right)

Step-by-step solution

If P is a point on the parabola y = x ^ 2 + 4 which is closest to the straight line y = 4x - 1, then the co-ordinates

P:y=x2+4P: y = {x}^{2} + 4

k=h2+4k = {h}^{2} + 4

L:y=4x−1L: y = 4x - 1

y−4x+1=0y - 4x + 1 = 0

D=AB=∣k−4h+117∣=∣h2+4−4h+117∣D = AB = \left|\dfrac{k - 4h + 1}{\sqrt{17}}\right| = \left|\dfrac{{h}^{2} + 4 - 4h + 1}{\sqrt{17}}\right|

d(D)dh=2h−417=0\dfrac{d\left(D\right)}{dh} = \dfrac{2h - 4}{\sqrt{17}} = 0

h=2h = 2

d2(D)dh2=217>0\dfrac{{d}^{2}\left(D\right)}{d{h}^{2}} = \dfrac{2}{\sqrt{17}} > 0

∴k=4+4=8∴ k = 4 + 4 = 8

∴∴ Point \left(2, 8\right)

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