Q17 / 53 · NTA Abhyas (JEE Main) 2020 · Mathematics · Ellipse

If y=x+c touches the ellipse 3x2+4y2=12 at the point P, then the value of the length OP (where O is the origin) is equal to

  • A
    3 units
  • B
    7 units
  • Correct answer
    C
    57 units
  • D
    75 units

Solution

If y=x+c touches x24+y23=1

then, c=±41+3

=±7

Let's assume, c=7  and y=x+7 touches x24+y23=1 at h,k.

then, xh4+yk3=1 is same as y-x=7

⇒h4-1=k31=17

⇒h,k=-47,37=P

Hence, OP=167+97=57 units

Hence, the correct answer is option: 'C'.

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