Q22 / 109 · NTA Abhyas (JEE Main) 2020 · Mathematics · Straight Lines

Let P≡a,0, Q≡-1,0 and R≡2,0 are three given points. If the locus of the point S satisfying the relation SQ2+SR2=2SP2 is 2x+3=0, then the sum of all possible values of a is

  • A
    1
  • B
    -4
  • C
    3
  • Correct answer
    D
    -3

Solution

We have, P≡a,0,Q≡-1,0,R≡2,0 .

Let, S≡x,y
Now, given that SQ2+SR2=2SP2. Hence,
x+12+y2+x-22+y2=2x-a2+y2
or 2x2+2y2-2x+5=2x2+2y2-4ax+2a2
or 4a-2x=2a2-5 or 2x+3=0
or x=-32=2a2-54a-2

⇒a=1,-4

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

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