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      <text>7.2.3.7 Introducing the identity matrix</text>
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      <text><![CDATA[<h4>The identity matrix</h4>
<p>The matrix \(\begin{bmatrix}1 & 0 \\ 0 & 1\end{bmatrix}\) is called the <b>identity matrix</b> or <b>unit matrix</b> of order 2, and is usually denoted by the symbol \(I.\) (Strictly we should write \(I_{2},\) to indicate the size.) The matrix \(I\) plays the same role in matrix multiplication as the number \(1\) does in number multiplication.</p>
<p> Hence, just as \[ a \times 1 = 1 \times a = a \qquad \text{ for any number } a, \] so \[ AI = IA = A \qquad \text{ for any matrix } A. \]</p>]]></text>
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