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JEE Main 202228 JulyEvening Shift
Exam
JEE Main
Year
2022
Date
28 July
Shift
Evening Shift
Subject
Mathematics
Chapter
Hyperbola

JEE Main 2022 · 28 July · Evening Shift · Mathematics · Hyperbola

Let the hyperbola H: x ^ 2 a ^ 2 - y ^ 2 b ^ 2 = 1 pass through the...

Let the hyperbola H:x2a2−y2b2=1H: \dfrac{{x}^{2}}{{a}^{2}} - \dfrac{{y}^{2}}{{b}^{2}} = 1 pass through the point \left(2\sqrt{2}, - 2\sqrt{2}\right).Aparabolaisdrawnwhosefocusissameasthefocusof. A parabola is drawn whose focus is same as the focus ofHwithpositiveabscissaandthedirectrixoftheparabolapassesthroughtheotherfocusofwith positive abscissa and the directrix of the parabola passes through the other focus ofH.Ifthelengthofthelatusrectumoftheparabolaisetimesthelengthofthelatusrectumof. If the length of the latus rectum of the parabola is e times the length of the latus rectum ofH,where, wheree is the eccentricity of HH, then which of the following points lies on the parabola?

Options

  1. A(23,32)\left(2\sqrt{3}, 3\sqrt{2}\right)
  2. B(33,−62)\left(3\sqrt{3}, - 6\sqrt{2}\right)
  3. C(3,−6)\left(\sqrt{3}, - \sqrt{6}\right)
  4. D(36,62)\left(3\sqrt{6}, 6\sqrt{2}\right)

Correct answer

B. (33,−62)\left(3\sqrt{3}, - 6\sqrt{2}\right)

Step-by-step solution

Given,

H:x2a2−y2b2=1H: \dfrac{{x}^{2}}{{a}^{2}} - \dfrac{{y}^{2}}{{b}^{2}} = 1

So coordinates of foci will be : S(ae,0),S′(−ae,0)S\left(ae, 0\right), {S}^{'}\left(- ae, 0\right)

Now foot of directrix of parabola will be \left(- ae, 0\right)</p><p>Alsofocusofparabolaiswhichissameasfocusof</p><p>Also focus of parabola is which is same as focus ofHwillbe(ae,0)will be \left(ae, 0\right)

Now, semi latus rectum of parabola =\left|S{S}^{'}\right| = 2ae</p><p>Given,</p><p>Given,4ae = e\left(\dfrac{2{b}^{2}}{a}\right)</p><p></p><p>⇒ {b}^{2} = 2{a}^{2} . . . \left(1\right)</p><p>Alsogiven,(22,−22)</p><p>Also given, \left(2\sqrt{2}, - 2\sqrt{2}\right) lies on H:x2a2−y2b2=1H: \dfrac{{x}^{2}}{{a}^{2}} - \dfrac{{y}^{2}}{{b}^{2}} = 1

⇒(22)2a2−(22)2b2=1⇒ \dfrac{{\left(2\sqrt{2}\right)}^{2}}{{a}^{2}} - \dfrac{{\left(2\sqrt{2}\right)}^{2}}{{b}^{2}} = 1

⇒1a2−1b2=18...(2)⇒ \dfrac{1}{{a}^{2}} - \dfrac{1}{{b}^{2}} = \dfrac{1}{8} . . . \left(2\right)

Now from equation \left(1\right) \text{ and } \left(2\right)weget,</p><p>we get,</p><p>{a}^{2} = 4, {b}^{2} = 8</p><p></p><p>∵ {b}^{2} = {a}^{2}\left({e}^{2} - 1\right)</p><p></p><p>∴ e = \sqrt{3}</p><p>So,theequationofparabolais</p><p>So, the equation of parabola is{y}^{2} = 4 \times \left(ae\right)x$⇒y2=83x⇒ {y}^{2} = 8\sqrt{3}x

So, only \left(3\sqrt{3}, - 6\sqrt{2}\right)willsatisfytheparabolawill satisfy the parabola{y}^{2} = 8\sqrt{3}x$

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