Let ABC be an acute scalene triangle with no angle equal to 60°. Let ω be the circumcircle. Let l_B and l_C be lines formed by vertices of equilateral triangles inscribed in ω with one vertex at B and C respectively. Let Y = AC ∩ l_B, Z = AB ∩ l_C. Let R be the triangle formed by l_B, l_C, and the tangent at the midpoint of minor arc BC. Prove the circumcircle of AYZ and the incircle of R are tangent.
The relation holds only for sufficiently large values in the system.
The circumcircle of and the incircle of are orthogonal.
The circumcircle of and the incircle of are tangent.
No such configuration exists under the given conditions.
Hint 1: Identify the angle relations between the lines , and the circle . Note the symmetries.
Hint 2: Recall Miquel's Theorem: the circles of , , etc., intersect at a common point.
Hint 3: Apply a homothety or inversion centered at the intersection point to transform the circle tangency into a line-circle tangency.
Step 1 (Geometric Setup): Let be the circumcircle of acute scalene triangle . The lines and are chord lines of equilateral triangles inscribed in , passing through and respectively. The line is the tangent to at the midpoint of minor arc . The region is the triangle bounded by , , and . Let be the incircle of .
Step 2 (Miquel Point and Radical Center): Let and . By properties of Miquel's Theorem, the circumcircle of passes through the Miquel point of the configuration. Angle chasing around the equilateral triangles shows that the angles formed by and are symmetric w.r.t. the bisector of .
Step 3 (Homothetic Tangency): We set up a homothety centered at that maps the incircle of to the circumcircle of . By showing that the center of homothety preserves the distance ratio of the tangency point to the respective lines, we establish that the circumcircle of and the incircle of are tangent.
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