Euclidean isometries and orthogonal matrices
Every distance-preserving bijection of ℝⁿ has form T(x)=Qx+b with QᵀQ=I; conversely each such map is an isometry.
Key knowledge
Every distance-preserving bijection of ℝⁿ has form T(x)=Qx+b with QᵀQ=I; conversely each such map is an isometry. It preserves distances and inner products of displacement vectors, hence angles. These transformations form the Euclidean isometry group.
Values and equations
‖T(x)−T(y)‖=‖x−y‖; (Qu)·(Qv)=u·v
- T
- Euclidean isometry x↦Qx+b
- Q
- Real square orthogonal matrix
- x,y
- Points of ℝⁿ
- u,v
- Displacement vectors
Conditions and scope
- Use the standard real Euclidean inner product and finite n≥1.
- The translation changes position-vector inner products about a fixed origin; the invariants concern differences T(x)−T(y)=Q(x−y). Orthogonal Q may reverse orientation.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Reinhard Schultz / University of California, Riverside2 sources
Evidence and review
Section 1 first isometry theorem and proof, printed pages 1–2; affineGeometry isometry definition, Proposition 3 and orthogonal/translation examples, printed pages 67–68.
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