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JEE Mains · Maths · STD 11 - 10.2 parabola,ellipse,hyperbola

Let \(x=2 t, y=\frac{i}{3}\) be a conic. Let \(S\) be the focus and \(B\) be the point on the axis of the conic such that \(SA \perp BA\), where \(A\) is any point on the conic. If \(k\) is the ordinate of the centroid of \(\Delta SAB\), then \(\lim _{ t \rightarrow 1} k\) is equal to

  1. A \(\frac{17}{18}\)
  2. B \(\frac{19}{18}\)
  3. C \(\frac{11}{18}\)
  4. D \(\frac{13}{18}\)
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Answer & Solution

Correct Answer

(D) \(\frac{13}{18}\)

Step-by-step Solution

Detailed explanation

parabola \(x ^{2}=12 y\) \(SA \perp SB\) so, \(m _{ AS } \cdot m _{ AB }=-1\) \(\frac{\left(3-\frac{ t ^{2}}{3}\right)}{(0-2 t )} \cdot \frac{\left(\alpha-\frac{ t ^{2}}{3}\right)}{(0-2 t )}=-1\) by solving \(3 \alpha=\frac{27 t^{2}+t^{4}}{t^{2}-9}\) ordinate of centriod of…
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