第13题: [单项选择]A. It will allow fewer trees to be cut. B. It will require less labor costs. C. It saves some shipping costs. D. It will make them more competitive. 参考答案:C 答案解析:[听力原文] Why does the speaker believe the system mayr also be beneficial to exporters
第15题: [单项选择]已知3阶阵A的特征值为1,-1,2,设矩阵B=A3-5A2,则正确的为______。 A. B的特征值为-4,-6,12 B. B的特征值为-4,-6,-12 参考答案:B 答案解析:[解析] (1)设A的特征值为λ,对应特征向量为x,即Ax=λx,则λ3-5λ2为A3-5A2的一个特征值,所以