IMO 2025 Problem 2
- Day 1
- Geometry
- Proof
Let and be circles with centres and , respectively, such that the radius of is less than the radius of . Suppose circles and intersect at two distinct points and . Line intersects at and at , such that points , , and lie on the line in that order. Let be the circumcentre of triangle . Line intersects again at . Line intersects again at . Let be the orthocentre of triangle .
Prove that the line through parallel to is tangent to the circumcircle of triangle .
(The orthocentre of a triangle is the point of intersection of its altitudes.)
Official text IMO 2025 official English paper, page 1. Quoted with source.
Solutions
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