单选题设n阶矩阵A的行列式|A|=a≠0(n≥2)，λ是A的一个特征值，A * 为A的伴随矩阵

单选题甲、乙两组射手打靶，两组射手的平均成绩是150环。(1)甲组的人数比乙组人数多20％。(2)乙组的平均成绩是171．6环，比甲组的平均成绩高30％。

单选题A是4阶矩阵，设A=(α1，α2，α3，α4)，其中向量组α2，α3，α4线性无关，且α1-3α2-2α3，则齐次线性方程组AX=0______。 A．有非零解，且通解为X=k(1，-3，2，0)T(k为任意实数) B．有非零解，且通解为X=k(1，-3，-2)T(k为任意实数) C．有非零解，且通解为X=k(1，-2，3，1)T(k为任意实数) D．只有零解

单选题如下图所示，一个底面半径为R的圆柱形量杯中装有适量的水．若放入一个半径为r的实心铁球，水面高度恰好升高r，则A．B．C．D．E．

单选题微分方程y"-7y'+12y=0的通解是( )。A．y=Ce3xB．y=Ce4xC．y=e3x(C1cos 4x+C2sin 4x)D．y=C1e3x+C2e4x

单选题设f(x)可导，且F(x)=f(x)(1+|sinx|)在x=0处可导，则______.

单选题[2011年1月]现有一批文字材料需要打印，两台新打印机单独完成此任务分别需要4小时与5小时，两台旧型打印机单独完成任务分别需要9小时与11小时。则能在2．5小时内完成此任务。 (1)安排两台新型打印机同时打印： (2)安排一台新型打印机与两台旧型打印机同时打印。

单选题某单位有男职工420人，男职工人数是女职工人数的倍，工龄20年以上者占全体职工人数的20%，工龄10～20年者是工龄10年以下者人数的一半，工龄在10年以下者人数是______．

单选题For the past two years in Silicon Valley, the centre of America's technology industry, conference-goers have entertained themselves playing a guessing game: how many times will a speaker mention the phrase "long tail"? It is usually a high number, thanks to the influence of the long-tail theory, which was first developed by Chris Anderson, the editor of Wired magazine, in an article in 2004. Though technologists and bloggers chuckle at how every business presentation now has to have its long-tail section, most are envious of Mr. Anderson, whose brainwave quickly became the most fashionable business idea around. Whether a blockbuster film, a bestselling novel, or a chart-topping rap song, popular culture idolises the hit. Companies devote themselves to creating them because the cost of distribution and the limits of shelf space in physical shops mean that profitability depends on a high volume of sales. But around the beginning of this century a group of internet companies realised that with endless shelves and a national or even international audience online they could offer a huge range of products—and make money at the same time. The niche, the obscure and the specialist, Mr. Anderson argues, will gain ground at the expense of the hit. As evidence, he points to a drop in the number of companies that traditionally calculate their revenue/sales ratio according to the 80/20 rule—where the top fifth of products contribute four-fifths of revenues. Ecast, a San Francisco digital jukebox company, found that 98% of its 10000 albums sold at least one track every three months. Expressed in the language of statistics, the experiences of Ecast and other companies such as Aragon, an online bookseller, suggest that products down in the long tail of a statistical distribution, added together, can be highly profitable. The internet helps people find their way to relatively obscure material with recommendations and reviews by other people, (and for those willing to have their artistic tastes predicted by a piece of software) computer programs which analyse past selections. Long-tail enthusiasts argue that the whole of culture will benefit, not just commercial enterprises. Television, film and music are such bewitching media in their own right that many people are quite happy to watch and listen to what the mainstream provides. But if individuals have the opportunity to pick better, more ideally suited entertainment from a far wider selection, they will take it, according to the theory of the long tail. Some analysts reckon that entire populations might become happier and wiser once they have access to thousands of documentaries, independent films and subgenres of every kind of music, instead of being subjected to what Mr. Anderson calls the tyranny of lowest-common-denominator fare. That might be taking things a bit far. But the long tail is certainly one of the internet's better gifts to humanity.

单选题设函数f(x)在闭区间[-1，1]上具有三阶连续导数，且f(-1)=0，f(1)=1，f'(0)=0，证明：在开区间(-1，1)内至少存在一点ξ，使f"'(ξ)=3．

单选题为()

单选题如图，在直角坐标系xOy中，矩形OABC的顶点B的坐标是(6，4)，则直线l将矩形OABC分成了面积相等的两部分。(1)l：x—y—1=0。(2)l：x一3y+3=0。

单选题设f(x，y)为连续函数，交换积分次序后得到______A．B．C．D．

单选题设，则f(x)在x=a处______