MathDB
Construction and calculation in a pyramid

Source: Czech and Slovak Olympiad 1957, National Round, Problem 2

April 10, 2020
geometrycomputational geometryconstructive geometry3D geometrypyramidnational olympiad

Problem Statement

Consider a (right) square pyramid ABCDVABCDV with the apex VV and the base (square) ABCDABCD. Denote d=AB/2d=AB/2 and φ\varphi the dihedral angle between planes VADVAD and ABCABC. (1) Consider a line XYXY connecting the skew lines VAVA and BCBC, where XX lies on line VAVA and YY lies on line BCBC. Describe a construction of line XYXY such that the segment XYXY is of the smallest possible length. Compute the length of segment XYXY in terms of d,φd,\varphi. (2) Compute the distance vv between points VV and XX in terms of d,φ.d,\varphi.