Q55 / 125 · BITSAT 2017 · Mathematics

If two distinct chords drawn from the point (p,q) on the circle x2+y2=px+qy (where pq≠0) are bisected by the X-axis, then

  • A
    p2=q2
  • B
    p2=8q2
  • C
    p2<8q2
  • Correct answer
    D
    p2>8q2

Solution

Let (t, m) be the other end of the chord drawn from the point (p, q) on the circle

x2+y2=px+qy

Their mid-point is t+p2,m+q2

since, mid-point lies on X-axis i.e. y=0

m+q=0   ...(i)

Also, (t, m) lies on the circle.

∴ t2+m2-pt-qm=0   ...(ii)

From Eqs. (i) and (ii), we get t2-pt+2q2=0

Which is quadratic in t such that, Discriminant >0

⇒ p2-8q2>0⇒p2>8q2

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

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