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JEE Main 20199 JanuaryEvening Shift
Exam
JEE Main
Year
2019
Date
9 January
Shift
Evening Shift
Subject
Mathematics
Chapter
Parabola

JEE Main 2019 · 9 January · Evening Shift · Mathematics · Parabola

Let A(4, - 4) and B(9, 6) be points on the parabola, y ^ 2 = 4x ....

Let A(4,−4)A\left(4, - 4\right) and B(9,6)B\left(9, 6\right) be points on the parabola, y2=4x.{y}^{2} = 4x . Let CC be chosen on the arc AOBAOB of the parabola, where OO is the origin, such that the area of δACB\delta ACB is maximum. Then, the area (in sq. units)ofδACBof \delta ACB , is:Let A(4, - 4) and B(9, 6) be points on the parabola, y ^ 2 = 4x . Let C be chosen on the arc AOB of the parabola, where

Options

  1. A3232
  2. B313431\dfrac{3}{4}
  3. C301230\dfrac{1}{2}
  4. D311431\dfrac{1}{4}

Correct answer

D. 311431\dfrac{1}{4}

Step-by-step solution

Let the coordinates of CC be \left({t}^{2}, 2t\right).<br/><br/>Areaof.<br /><br />Area of∆ ABC = \dfrac{1}{2}\left|{t22t19614−41\begin{cases}{t}^{2} & 2t & 1 \\ 9 & 6 & 1 \\ 4 & - 4 & 1\end{cases}\right|<br/><br/><imgsrc="https://cdn−question−pool.getmarks.app/pyq/jeemain/fxxbaheoukaahekknvirjtznwxhovcyerjqkiutjvxiatyvuff.png"/><br/><br/><br /><br /><img src="https://cdn-question-pool.Quantrex.app/pyq/jee_main/fxxbaheoukaahekknvirjtznwxhovcyerjqkiutjvxiatyvuff.png" /><br /><br />∆ = 5\left|\left(6 + t - {t}^{2}\right)\right|, t∈(−2,3)t \in \left(- 2, 3\right)

d∆dt=1−2t=0⇒t=12\dfrac{d ∆}{dt} = 1 - 2t = 0 ⇒ t = \dfrac{1}{2}

d2△dt2=−2\dfrac{{d}^{2} △}{d{t}^{2}} = - 2, hence area is maximum at t=12t = \dfrac{1}{2}

∴ {\Delta}_\max = \dfrac{125}{4} = 31\dfrac{1}{4}

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