四面体是面数最少的多面体,它的四个面都是三角形,四面中有一面、二面或三面是直角三角形的四面体是存在的,那么四面能否都是直角三角形呢? 把四面体的顶点看作三面角的顶点,则四面体内含四个三面角.以三面角的三个面角等于直角的个数(最多者)进行讨论. 1.直三面角 A tetrahedron is a polyhedron with the fewest number of faces. Its four faces are all triangles. A tetrahedron with four faces, two faces, or three faces with right-angled triangles is present. Is it possible that all four sides are right-angled triangles? The apex of the triangle is considered as the vertex of the trihedral angle, then the tetrahedron contains four trihedral angles. The three face angles of the trihedral angle are equal to the number of right angles (the most). 1. Straight trihedral angle