单选题设，A*是A的伴随矩阵，则(A*)-1=______．

单选题由相交于三点(x1，y1)，(x2，y2)，(x3，y3)(其中x1＜x2＜x3)的两曲线y=f(x)＞0，y=g(x)＞0所围成的图形绕x轴旋转一周所得旋转体体积为A．．B．．C．．D．．

单选题设A，B是n阶可逆矩阵，满足AB=A+B． 则①|A+B|=|A||B|； ②(AB)-1=A-1B-1； ③(A-E)X=0只有零解； ④B-E不可逆． 中正确的个数是 {{U}} {{/U}}． A.1． B.2． C.3． D.4．

单选题The European Union's Barcelona summit, which ended on March 16th, was played out against the usual backdrop of noisy "anti-globalization" demonstrations and massive security. If nothing else, the demonstrations illustrated that economic liberalization in Europe--the meeting's main topic--presents genuine political difficulties. Influential sections of public opinion continue to oppose anything that they imagine threatens "social Europe", the ideal of a cradle-to-grave welfare state. In this climate of public opinion, it is not surprising that the outcome in Barcelona was modest. The totemic issue was opening up Europe's energy markets. The French government has fought hard to preserve a protected market at home for its state-owned national champion, Electricite de France (EDF). At Barcelona it made a well-flagged tactical retreat. The summiteers concluded that from 2004 industrial users across Europe would be able to choose from competing energy suppliers, which should account for "at least" 60% of the market. Since Europe's energy market is worth 350 billion ( $ 309 billion) a year and affects just about every business, this is a breakthrough. But even the energy deal has disappointing aspects. Confining competition to business users makes it harder to show that economic liberalization is the friend rather than the foe of the ordinary person. It also allows EDF to keep its monopoly in the most profitable chunk of the French market. In other areas, especially to do with Europe's tough labor markets, the EU is actually going backwards. The summiteers declared that "disincentives against taking up jobs" should be removed; 20m jobs should be created within the EU by 2010. But only three days after a Barcelona jamboree, the European Commission endorsed a new law that would give all temporary-agency workers the same rights as full-timers within six weeks of getting their feet under the desk. Six out of 20 commissioners did, unusually, vote against the measure--a blatant piece of re-regulation--but the social affairs commissioner, Anna Diamantopoulou, was unrepentant, indeed triumphant. A dissatisfied liberaliser in the commission called the directive "an absolute disaster". The summit's other achievements are still more fragile. Europe's leaders promised to increase spending on "research and development" from its current figure of 1.9% of GDP a year to 3%. But how will European politicians compel businesses to invest more in research? Nobody seems to know. And the one big research project agreed on at Barcelona, the Galileo satellite-positioning system, which is supposed to cost 3.2 billion of public money, is of dubious commercial value, since the Europeans already enjoy free access to the Americans' GPA system. Edward Bannerman, head of economics at the Centre for European Reform, a Blairite think-tank, calls Galileo "the common agricultural policy in space./

单选题设A，B是n阶可逆矩阵，满足AB=A+B． 则①|A+B|=|A||B|； ②(AB)-1=A-1B-1； ③(A-E)X=0只有零解； ④B-E不可逆． 中正确的个数是 ( )．

单选题下列命题中正确的是A．设正项级数发散，则．B．设收敛，则收敛．C．设中至少一个发散，则发散．D．设收敛，则均收敛．

单选题下列等式正确的是(A)(B)(C)(D)

单选题设级数发散，则级数

单选题设α1，α2，α3，α4为四维非零列向量，A=[α1，α2，α3，α4]，A*为A的伴随矩阵，又知方程组AX=0的基础解系为[-1，0，2，0]T，则方程组A*X=0的基础解系为______． A．α1，α2，a3 B．α1+α2，α2+α3，α3+α1 C．α2，α3，α4 D．α1+α2，α2+α3，α3+α4，α4+α1

单选题设积分区域D={(x，y)|x2+y2≤1)；D1={(x，y)|x2+y2≤1，x≥0，y≥0)．在如下的四个等式①．②．③④中不成立的是A.①．B.②．C.③．D.④．

单选题n阶矩阵A具有n个不同的特征值是A与对角矩阵相似的 (A) 充分必要条件． (B) 充分而非必要条件． (C) 必要而非充分条件． (D) 既非充分也非必要条件．

单选题设随机变量X与Y相互独立，且则概率P{|X-Y|＜1}______

单选题已知2n阶行列式D的某一列元素及其余子式都等于a，则D= A.0． B.a2． C.-a2． D.na2．