[1 -1 1]设矩阵 A=[1 3 -1][11 1]的三个特征值分别为 λ 1, λ 2, λ 3,则 λ 1+ λ 2+ λ 3= ( )
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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