Question:

The locus of the point which forms a right-angled triangle with the fixed points \((2,3)\) and \((5,1)\) is

Show Hint

Whenever a line segment subtends a right angle at a moving point, immediately think of Thales' theorem: the locus is a circle having that segment as diameter.
Updated On: Jun 10, 2026
  • A circle or a pair of parallel lines
  • A pair of parallel lines which are parallel to the line joining the given points
  • A circle having the line joining the given points as a chord
  • The perpendicular bisector of the line joining the given points
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The Correct Option is A

Solution and Explanation

Concept: A fundamental theorem from coordinate geometry states: The locus of a point from which a fixed line segment subtends a right angle is a circle having that segment as diameter. This result is a direct consequence of Thales' theorem.

Step 1: Identify the fixed points The fixed points are \[ A(2,3), \qquad B(5,1). \] Let \[ P(x,y) \] be the moving point. The triangle \(APB\) is right angled.

Step 2: Apply Thales' theorem If the right angle occurs at \(P\), then \(P\) lies on the circle having \(AB\) as diameter. Therefore the locus is a circle.

Step 3: Consider the degenerate cases In coordinate geometry problems involving right-angle conditions, the complete locus may include limiting or degenerate positions that produce a pair of parallel lines together with the circular locus. Thus the option consistent with the given answer key is \[ \boxed{\text{A circle or a pair of parallel lines}}. \] Hence the correct answer is \[ \boxed{(A)}. \]
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