正せい四し面めん体たい

noun

regular tetrahedron

A polyhedron with four congruent equilateral triangular faces; a fundamental shape in geometry.

• 正せい四し面めん体たいの体たい積せきを求もとめる公こう式しきを覚おぼえていますか。

  Do you remember the formula for the volume of a regular tetrahedron?