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JEE Main 20188 April
Exam
JEE Main
Year
2018
Date
8 April
Subject
Mathematics
Chapter
Parabola

JEE Main 2018 · 8 April · Mathematics · Parabola

Tangent and normal are drawn at P(16, 16) on the parabola y ^ 2 =...

Tangent and normal are drawn at $P(16,16)P\left(16, 16\right) on the parabola y2=16x{y}^{2} = 16x, which intersect the axis of the parabola at A and BA \text{ and } B, respectively. If CC is the center of the circle through the points P,A and BP, A \text{ and } B and ∠CPB=θ,∠CPB = \theta, then a value of $tan \theta is:Tangent and normal are drawn at P(16, 16) on the parabola y ^ 2 = 16x , which intersect the axis of the parabola at A

Options

  1. A43\dfrac{4}{3}
  2. B12\dfrac{1}{2}
  3. C22
  4. D33

Correct answer

C. 22

Step-by-step solution

Tangent and normal are drawn at P(16, 16) on the parabola y ^ 2 = 16x , which intersect the axis of the parabola at A

Equation of tangent at (x1,y1)\left({x}_{1}, {y}_{1}\right) is yy1=2a(x+x1)y{y}_{1} = 2a\left(x + {x}_{1}\right)

Equation of normal at \left({x}_{1}, {y}_{1}\right)isisy - {y}_{1} = - \dfrac{{y}_{1}}{2a} ( x - {x}_{1} )<br/><br/>Heretangentandnormalpassesthrough<br /><br />Here tangent and normal passes throughP ( 16, 16 )<br/><br/><br /><br />∴EquationoftangentisEquation of tangent is2y = x + 16<br/><br/>Equationofnormalis<br /><br />Equation of normal isy + 2x = 48<br/><br/>Tangentandnormalintersectx−axisat<br /><br />Tangent and normal intersect x-axis atA\left(- 16, 0\right)andandB ( 24, 0 )<br/><br/>Since,<br /><br />Since,APBisarightangledtriangle,henceis a right angled triangle, henceABisthediameterforthecircle.</p><p>Alsomidpointofis the diameter for the circle.</p><p>Also mid point ofABiscenterofthecircle.<br/><br/>HenceCentreis center of the circle.<br /><br />Hence Centre= \left(4, 0\right)<br/><br/>Slopeof<br /><br />Slope ofPC = \dfrac{4}{3}<br/><br/>Slopeof<br /><br />Slope ofPB$=−2= - 2

$tan \theta = \left|\dfrac{\dfrac{4}{3} + 2}{1 - 2 \times \dfrac{4}{3}}\right| = \left|\dfrac{10}{- 5}\right| = 2

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