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\left| {\begin{array}{*{20}{c}}i & j & k\\1 & { - 2} & 3\\2 & 1 & 2\\\end{array}} \right| = i\left| {\begin{array}{*{20}{c}}{ - 2} & 3\\1 & 2\\\end{array}} \right| - j\left| {\begin{array}{*{20}{c}}1 & 3\\2 & 2\\\end{array}} \right| + k\left| {\begin{array}{*{20}{c}}1 & { - 2}\\2 & 1\\\end{array}} \right| = - 7i + 4j + 5k