Linear algebra - Orthogonal matrix

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SUMMARY

The discussion centers on proving that a linear transformation T: Rn -> Rn preserves vector lengths if and only if its B-matrix representation [T]B is an orthogonal matrix. An orthogonal matrix satisfies the condition T-1 = TT, indicating that the inverse of the transformation equals its transpose. The key to the proof lies in expressing the preservation of vector lengths in terms of matrix equations, specifically focusing on the squared lengths of vectors.

PREREQUISITES
  • Understanding of linear transformations
  • Familiarity with orthonormal bases
  • Knowledge of matrix representations
  • Concept of orthogonal matrices
NEXT STEPS
  • Study the properties of orthogonal matrices in linear algebra
  • Learn about the implications of preserving vector lengths under transformations
  • Explore the relationship between matrix transposes and inverses
  • Investigate examples of linear transformations that are not orthogonal
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Students and educators in linear algebra, mathematicians focusing on transformations, and anyone seeking to deepen their understanding of orthogonal matrices and their properties.

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Homework Statement


Let T: Rn -> Rn be a linear transformation, and let B be an orthonormal basis for R^n. Prove that [ the length of T(x) ] = [ the length of x ] if and only if [T]B (the B-matrix for T) is an orthogonal matrix.


Homework Equations


None I don't think.


The Attempt at a Solution


I've always had a hard time grasping linear transformation problems, so I don't even really know where to start with this one.
 
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A transformation is orthogonal if its matrix representation obeys a certain equation. In an orthonormal basis, this equation reduces to T-1=TT. (It's inverse is equal to its transpose.) So that's one relevant equation. How would you express, as a matrix equation, the fact that the length of a vector is unchanged by a transformation? Hint: if the length stays the same, what can we say about the square of the length?
 

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