16 lines
145 B
TeX
16 lines
145 B
TeX
\parindent=0pt
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Invert a $2\times2$ matrix by inspection.
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$$\pmatrix{
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a&b\cr
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c&d\cr
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}^{-1}
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=
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{1\over ad-bc}
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\pmatrix{
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d&-b\cr
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-c&a\cr
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}$$
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\end
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