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section of triangle with any plane is right triangle.

Source: Polish MO Second Round 1964 p5

August 31, 2024
geometry3D geometryright triangle

Problem Statement

Given is a trihedral angle with edges SA SA , SB SB , SC SC , all plane angles of which are acute, and the dihedral angle at edge SA SA is right. Prove that the section of this triangle with any plane perpendicular to any edge, at a point different from the vertex S S , is a right triangle.
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