20.(2013中山)一IsawTonyattheparty.Buthedidn’tspeaktomeevening.—Maybehedidn’tseeyou.A.allB.everyC.eitherD.another
20.(2013 中山) 一I saw Tony at the party. But he didn’t speak to me evening.
—Maybe he didn’t see you.
A. all B. every C. either D. another
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n阶方阵A对任意n维向量x,满足x^TAx=0,充要条件为AT=-A；证明：充分性：f=x^TAx 2020-05-17 …
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设A为奇数阶实对称矩阵,且det(A)>0.求证：存在非零向量X,满足X∧T*A*X>0 2020-06-22 …
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函数f(x)的定义域为D,若满足如下两条件:①f(x)在D内是单调函数;②存在[m/2,n/2]是D 2021-01-04 …