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NDA 2021 Maths · Mathematics · Conic Sections · medium

The distance between the foci of the rectangular hyperbola x^2-y^2=8 is

Single correct option

The distance between the foci of the rectangular hyperbola x2−y2=8x^2-y^2=8 is
  1. A. 88
  2. B. 44
  3. C. 424\sqrt2
  4. D. 828\sqrt2
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Answer: (A) 88

Writing x28−y28=1\dfrac{x^2}{8}-\dfrac{y^2}{8}=1 gives a2=b2=8a^2=b^2=8, so c2=16c^2=16 and c=4c=4. The foci (±4,0)(\pm4,0) are 2c=82c=8 apart. The value 44 is the distance from the centre to one focus.
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Original question written in the NDA 2021 Maths pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake