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<h1> Inverse of a Matrix </h1>
 
<h1> Inverse of a Matrix </h1>
  
<p> An <i>n</i> x <i>n</i> matrix <i>A</i> is said to have an inverse provided there exists an <i>n</i> x <i>n</i> matrix <i>B</i> such that <i>AB</i> = <i>BA</i> = <i>I</i><sub>n</sub>.  We call <i>B</i> the inverse of <i>A</i> and denote it as <i>A</i><sup>-1</sup>.  Thus, <i>A</i><i>A</i><sup>-1</sup> = <i>A</i><sup>-1</sup><i>A</i> = <i>I</i><sub>n</sub>.  In this case, A is also called nonsingular.  
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<p> An <i>n</i> x <i>n</i> matrix <i>A</i> is said to have an inverse provided there exists an <i>n</i> x <i>n</i> matrix <i>B</i> such that <i>AB</i> = <i>BA</i> = <i>I</i><sub>n</sub>.  We call <i>B</i> the inverse of <i>A</i> and denote it as <i>A</i><sup>-1</sup>.  Thus, <i>A</i><i>A</i><sup>-1</sup> = <i>A</i><sup>-1</sup><i>A</i> = <i>I</i><sub>n</sub>.  In this case, A is also called nonsingular. </p>
  
  
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<h3> Theorem 1 </h3>
  
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<p> The inverse of a matrix, if it exists, is unique </p>
  
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<h3> Theorem 2 </h3>
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<p> If <i>A</i> and <i>B</i> are both nonsingular <i>n</i> x <i>n</i> matrices, then <i>AB</i> is nonsingular and (<i>AB</i><sup>)-1</sup> = <i>B</i><sup>-1</sup><i>A</i><sup>-1</sup>.
  
  

Revision as of 06:46, 10 December 2012

Inverse of a Matrix

An n x n matrix A is said to have an inverse provided there exists an n x n matrix B such that AB = BA = In. We call B the inverse of A and denote it as A-1. Thus, AA-1 = A-1A = In. In this case, A is also called nonsingular.


Theorem 1

The inverse of a matrix, if it exists, is unique

Theorem 2

If A and B are both nonsingular n x n matrices, then AB is nonsingular and (AB)-1 = B-1A-1.

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