已选分类
理学数学
单选题曲线______
单选题设f(x)为已知连续函数，，其中s＞0，t＞0，则I的值______A.依赖于s和t．B.依赖于s．t，x．C.依赖于t和x，不依赖于s．D.依赖于s，不依赖于t．
单选题已知曲线x2+y2=R2上一点(X，Y)，过点(X，Y)作曲线的切线，交坐标轴于A，B两点，AB线段为最短时，点(X，Y)的坐标为{{U}}{{/U}}．
单选题设A为n阶实对称矩阵，B为n阶可逆矩阵，Q为n阶正交矩阵，则下列矩阵与A有相同特征值的是
单选题
单选题设函数z=x2+y2+xy，则等于____。
单选题已知，则秩(A-E)+秩(A-3E)=______．A．7B．6C．5D．4
单选题
单选题[2011年1月]已知x2+y2=9，xy=4，则=()。
单选题
单选题若双曲线经过点，且它的两条渐近线的方程是，则双曲线方程是______。A．B．C．D．
单选题设A为n阶非零矩阵，E为n阶单位矩阵，若A3=O，则 (A)E-A不可逆，E+A不可逆. (B)E-A不可逆，E+A可逆. (C)E-A可逆，E+A可逆. (D)E-A可逆，E+A不可逆. [ ]
单选题烧杯中有1L纯酒精，倒出一定量的酒精后，再用水补充至原体积，然后再倒出和第一次一样多的酒精溶液，再用水补充至原体积，此时烧杯中酒精溶液的浓度变为64%，则两次共补充水的体积为______．
单选题设A是三阶矩阵，其中a11≠0，Aij=aij，i=1，2，3，j=1，2，3，则|2AT|=
A.0．
B.2．
C.4．
D.8．
单选题与矩阵合同的矩阵是
单选题设O为坐标原点，A、B在抛物线y2=2x上，OA⊥OB，且|OA|=|OB|，则△ABC的面积是( )．
单选题
单选题设f(x)连续，，则F"(x)等于
单选题
单选题These are tough times for Wal-Mart, America's biggest retailer. Long accused of (1) small-town America mad condemned for the selfishness of its pay, the company has lately come under (2) for its meanness over employees' health-care benefits. The charge is arguably (3) : the firm's health coverage, while (4) less extensive than the average for big companies, is on equal terms (5) other retailers'. But bad publicity, coupled with rising costs, has (6) the Bentonville giant to action. WalMart is making changes that should shift the ground in America's healthcare debate. One (7) is to reduce the prices of many generic, or out-of-patent, prescription drugs. Wal-Mart's critics dismiss the move as a publicity (8) . The list of drugs includes only 143 different medicines and excludes many popular group. True, but short-sighted. Wal-Mart has (9) retailing by using its size to squeeze suppliers and (10) the gains on to consumers. It could (11) the same with drugs. A "Wal-Mart effect" in drugs will not solve America's health-costs problem: group account for only a small share of drug costs, which in turn make (12) only 10% of overall health spending. But it would (13) . The firm's other initiative is more (14) . Wal-Mart is joining the small but fast-growing group of employers (15) are controlling costs by shifting to health insurance with high deductibles. Early evidence (16) these plans do help firms control the cost of health insurance. But critics say that the savings are (17) . They argue that the plans shift costs to sicker workers, discourage preventative care and will anyway do little to (18) overall health spending, (19) most of the $2 trillion that America (20) health care each year goes to people with multiple chronic diseases.