A positive-definite matrix is an important concept in linear algebra.

Kunminjōon is a book for teaching the correct pronunciation of Hangul.

A tesseract is a four-dimensional geometric shape.

The tesseract represents a four-dimensional geometric shape.

The 正五胞體 is a simple convex polytope in four dimensions, having five vertices.

A 5-cell is a simple convex polytope in four dimensions.

He made a model of a regular icosahedron.

He made a model of a regular dodecahedron.

This regular tetrahedron is composed of equilateral triangles on all sides.

A positive-semidefinite matrix is one of the important concepts in linear algebra.