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What conditions should hold for the four integers $n_1, n_2, m_1, m_2$ so that $(n_1, n_2)$ and $(m_1,m_2)$ can Z-linear span $Z^2$?

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    They span iff $n_1m_2-n_2m_1=\pm 1$.2012-08-30

2 Answers 2