HMMT 二月 2009 · 几何 · 第 2 题

HMMT February 2009 — Geometry — Problem 2

[ 3 ] The corner of a unit cube is chopped off such that the cut runs through the three vertices adjacent to the vertex of the chosen corner. What is the height of the cube when the freshly-cut face is placed on a table?

解析

[ 3 ] The corner of a unit cube is chopped off such that the cut runs through the three vertices adjacent to the vertex of the chosen corner. What is the height of the cube when the freshly-cut face is placed on a table? √ Answer: 2 3 / 3 √ Solution: The major diagonal has a length of 3. The volume of the pyramid is 1 / 6, and so its √ √ 1 3 2 height h satisfies · h · ( 2) = 1 / 6 since the freshly cut face is an equilateral triangle of side length 3 4 √ √