Let T be the line passing through the points P(–2, 7) and Q(2, –5). Let F 1 be the set of all pairs of circles (S 1 , S 2 ) such that T is tangent to S 1 at P and tangent to S 2 at Q, and also such that S 1 and S 2 touch each other at a point, say, M. Let E 1 be the set representing the locus of M as the pair (S 1 , S 2 ) varies in F 1 . Let the set of all straight line segments joining a pair of distinct points of E 1 and passing through the point R(1, 1) be F 2 . Let E 2 be the set of the mid-points of the line segments in the set F 2 . Then, which of the following statement(s) is (are) TRUE
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(b,d) 
Let C 1 and C 2 be the centre of circle S 1 and S 2 respectively
Let ∠ C 2 QM = ∠ C 2 MQ = θ ⇒ ∠ QC 2 M = π – 2 θ
Now vc ∠ QC 2 M + ∠ PC 1 M = π ⇒ π – 2 θ + π – 2 φ = π ⇒ θ + φ = π /2
Now vc ∠ QMP = π – ∠ QMC 2 – ∠ PMC 1 = π – ( θ + φ ) = π – π /2 = π /2
hence locus equation of variable point M is (x + 2)(x –2) + (y – 7)(y + 5) = 0
but locus of M does not contains point P and Q because P is included when radius of S 1 is zero and circle S 2 becomes straight line which is impossible. Q is included when radius of S 2 is zero and circle S 1 becomes straight line which is also impossible.
so set E 1 does not contain point P(–2, 7) and Q(2, – 5)
Locus of mid-points of chords passing through (1, 1) is h + K – (1 + k) = h 2 + k 2 – 2K
⇒ h 2 + K 2 – 2K – h + 1 = 0 ⇒ x 2 + y 2 – x – 2y + 1 = 0
Now equation of line passing through P(–2, 7) and R(1, 1) is
⇒ y + 2x – 3 = 0
Let centre of x 2 + y 2 – 2y – 39 = 0 is C 3 (0, 1) ⇒ centre of locus of M is C 3 (0, 1)
Now foot of C 3 (0, 1) on line y + 2x – 3 = 0 is
. which is mid-point of chord PR of circle
x 2 + y 2 – 2y – 39 = 0
But if P is not the part of locus of M then PQ is not the chord of locus of M.
So point
does not lies in set E 2
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