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Alderantzizko matrizea matrizea da, beste matrize batekin biderkatuta, emaitza gisa unitate matrizea ematen duena. Matrize karratuek bakarrik dute alderantziko matrizea, baina ez denek. A matrizearen alderantziko matrizea
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{\displaystyle A^{-1}}
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A
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I
n
{\displaystyle A\cdot A^{-1}=A^{-1}\cdot A=I_{n}}
I
n
{\displaystyle I_{n}}
n ordenako unitate matrizea den.
Determinante ez nulua daukan matrize bat emanik:
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a
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det
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{\displaystyle \mathbf {A} ^{-1}={\begin{bmatrix}a&b\\c&d\end{bmatrix}}^{-1}={\frac {1}{\det(\mathbf {A} )}}{\begin{bmatrix}\,\,\,d&\!\!-b\\-c&\,a\\\end{bmatrix}}={\frac {1}{ad-bc}}{\begin{bmatrix}\,\,\,d&\!\!-b\\-c&\,a\\\end{bmatrix}}}
Definituta dago
det
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=
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d
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c
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{\displaystyle {\det(\mathbf {A} )}=ad-bc\neq 0}
[
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↦
[
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,
{\displaystyle {\begin{bmatrix}2&1\\5&3\end{bmatrix}}\mapsto {\begin{bmatrix}2&1\\5&3\end{bmatrix}}^{-1}={\begin{bmatrix}3&-1\\-5&2\end{bmatrix}},}
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[
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=
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{\displaystyle {\begin{bmatrix}2&1\\5&3\end{bmatrix}}{\begin{bmatrix}3&-1\\-5&2\end{bmatrix}}={\begin{bmatrix}1&0\\0&1\end{bmatrix}}}
A
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{\displaystyle \mathbf {A} ^{-1}={\begin{bmatrix}a&b&c\\d&e&f\\g&h&i\\\end{bmatrix}}^{-1}={\frac {1}{\det(\mathbf {A} )}}{\begin{bmatrix}\,A&\,B&\,C\\\,D&\,E&\,F\\\,G&\,H&\,I\\\end{bmatrix}}^{T}={\frac {1}{\det(\mathbf {A} )}}{\begin{bmatrix}\,A&\,D&\,G\\\,B&\,E&\,H\\\,C&\,F&\,I\\\end{bmatrix}}}
Definituta dago
det
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A
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≠
0
{\displaystyle {\det(\mathbf {A} )}\neq 0}
A
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i
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f
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{\displaystyle {\begin{matrix}A=(ei-fh)&D=-(bi-ch)&G=(bf-ce)\\B=-(di-fg)&E=(ai-cg)&H=-(af-cd)\\C=(dh-eg)&F=-(ah-bg)&I=(ae-bd)\\\end{matrix}}}
Datuak: Q242188