PrepRung
Sign inSign up free

NDA 2017 Maths · Mathematics · Conic Sections · medium

A point on the parabola y^2=12x is at a distance 7 from the focus. Its abscissa is

Single correct option

A point on the parabola y2=12xy^2=12x is at a distance 77 from the focus. Its abscissa is
  1. A. 33
  2. B. 77
  3. C. 44
  4. D. 1010
Show answer and solution

Answer: (C) 44

Here 4a=124a=12, so a=3a=3 and the focus is (3,0)(3,0). The focal distance of (x,y)(x,y) is x+ax+a, so x+3=7x+3=7 and x=4x=4. The values 33 and 1010 come from forgetting to subtract or from adding aa again; 77 merely repeats the distance.
Report a mistake

Original question written in the NDA 2017 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