第3题: [单项选择]A. Less than 75 minutes. B. Two and a half hours. C. Two hours. D. More than 75 minutes. 参考答案:A 答案解析:[解析] W: How long did you have for the examination M: We were given two and a half hours,but
第9题: [单项选择]下列命题正确的是 A. 设A为n阶矩阵,A2=0,则A=0. B. 设A为"阶矩阵,A2=A,则A=0或A= C. 设A为n阶矩阵,AX=AY,A≠0,则X= D. 设A,B为n阶矩阵,且A为对称阵,则BTAB也为对称阵. 参考答案:D 答案解析:[分析] (A)的反例,可取[*], [*] (B) 的反例,可取[*],有A2但A≠0,A≠E. (C) 的反例,可取[*],有AX=AY,
第10题: [单项选择]可见光的波长范围是( ) A. 200~700nm B. 500~900nm C. 600~1000nm D. 400~800nm E. 200~500nm 参考答案:D