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BITSAT 2019
Exam
BITSAT
Year
2019
Subject
Mathematics
Chapter
Ellipse

BITSAT 2019 · Mathematics · Ellipse

The locus of the foot of perpendicular drawn from the centre of the...

The locus of the foot of perpendicular drawn from the centre of the ellipse x2+3y2=6x^{2} + 3y^{2} = 6 on any tangent to it is

Options

  1. A(x2−y2)2=6x2+2y2\left(x^{2} - y^{2}\right)2 = 6x^{2} + 2y^{2}
  2. B(x2−y2)2=6x2−2y2\left(x^{2} - y^{2}\right)2 = 6x^{2} - 2y^{2}
  3. C(x2+y2)2=6x2+2y2\left(x^{2} + y^{2}\right)2 = 6x^{2} + 2y^{2}
  4. D(x2+y2)2=6x2−2y2\left(x^{2} + y^{2}\right)2 = 6x^{2} - 2y^{2}

Correct answer

C. (x2+y2)2=6x2+2y2\left(x^{2} + y^{2}\right)2 = 6x^{2} + 2y^{2}

Step-by-step solution

We have,

x2+3y2=6x^{2} + 3y^{2} = 6

⇒x26+y22=1⇒ \dfrac{x2}{6} + \dfrac{y2}{2} = 1

Centre of an ellipse is~\left(0, 0\right).</p><p>Letthefootofperpendicularbe.</p><p>Let the foot of perpendicular be( h, k ).</p><p>Equationoftangentinslopeformtothestandardellipse .</p><p>Equation of tangent in slope form to the standard ellipse~\dfrac{x2}{a2} + \dfrac{y2}{b2} = 1 is</p><p>~is</p><p>y = mx \pm \sqrt{a^{2}m^{2} + b^{2}}.</p><p>Hence,equationoftangentwithslope.</p><p>Hence, equation of tangent with slopempassingpassing( h, k )is </p><p>is~</p><p>y = mx \pm \sqrt{6m^{2} + 2}</p><p></p><p>⇒ k = mh \pm \sqrt{6m^{2} + 2},where, wherem = - \dfrac{h}{k}.</p><p>.</p><p>⇒ k = h\left(- \dfrac{h}{k}\right) \pm \sqrt{6m^{2} + 2}</p><p></p><p>⇒ \sqrt{\dfrac{6h^{2}}{k2} + 2} = \dfrac{h^{2} + k^{2}}{k}</p><p></p><p>⇒ 6h^{2} + 2k^{2} = \left(h^{2} + k^{2}\right)2</p><p>So,requiredlocusis</p><p></p><p>So, required locus is</p><p>6x^{2} + 2y^{2} = \left(x^{2} + y^{2}\right)2.

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