2 lines intersect inside a regular triangular pyramid
Source: IV Soros Olympiad 1997-98 R3 11.11 https://artofproblemsolving.com/community/c2416727_soros_olympiad_in_mathematics
June 2, 2024
pyramidgeometry3D geometry
Problem Statement
An arbitrary point is taken on the basis of a regular triangular pyramid. Let , , be the projections of onto the lateral faces of this pyramid, and be the intersection point of the medians of the triangle . Prove that the straight line passing through the points and intersects the height of the pyramid (or its extension). Let us denote this intersection point by . Find if the dihedral angles at the base of the pyramid are equal to .