JEE Advanced · 2018 · 20 May 2018 · Paper 2 · Circle

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Let be the line passing through the points and . Let be the set of all pairs of circles such that is tangent to at and tangent to at , and also such that and touch each other at a point, say, . Let be the set representing the locus of as the pair varies in . Let the set of all straight line segments joining a pair of distinct points of and passing through the point be . Let be the set of the mid-points of the line segments in the set . Then, which of the following statement(s) is (are) TRUE?
  1. (A)The point lies in
  2. (B)The point does NOT lie in ✓ Correct
  3. (C)The point lies in
  4. (D)The point does NOT lie in ✓ Correct

Answer: (B), (D)

Solution

The locus of is a circle with center and radius , excluding points and :

Thus is excluded from the locus (it's point ), and checking : , so it does NOT lie in .

The locus of points in is a circle with diameter from to , excluding midpoints of chords through or :

The point is the center, which is excluded. The point is the midpoint of a chord through , so it does NOT lie in .

JEE Advanced · 2018 · 20 May 2018 · Paper 2 · One or more correct options

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