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Does an Orthogonal Matrix Have a Determinant?

Published in Linear Algebra 1 min read

Yes, every orthogonal matrix has a determinant.

Understanding Orthogonal Matrices

An orthogonal matrix is a square matrix whose columns and rows are orthonormal vectors. This means that each vector has a length of 1 (normalized), and they are all perpendicular to each other.

Determinants of Orthogonal Matrices

The determinant of an orthogonal matrix is always either +1 or -1. This property is directly linked to the orthonormality of its vectors.

  • Determinant = +1: The orthogonal matrix represents a rotation.
  • Determinant = -1: The orthogonal matrix represents a reflection.

Example

Consider the following orthogonal matrix:

[ 0  1 ]
[ -1  0 ] 

This matrix represents a rotation of 90 degrees counter-clockwise. Its determinant is:

(0 0) - (1 -1) = 1

Conclusion

Orthogonal matrices always have a determinant, and this determinant is either +1 or -1. This property is fundamental to understanding the geometric transformations represented by orthogonal matrices.

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