问答题计算二重积分其中D是由x2+y2=1的上半圆与x2+y2=2y的下半圆围成的区域．

问答题求曲线的拐点．

问答题设∫xf(x)dx=arcsinx+C，求．

问答题今有2n个同型号电子元件设计以两种不同方案组装在线路中(见图1与图2)．假设各元件独立工作且它们都服从期望值为1(单位：万小时)的指数分布，试比较两个不同方案的线路正常工作的平均时间．

问答题设直线y＝x＋1是曲线y＝x³＋3x²＋4x＋a的切线，求切点坐标和a的值。

问答题求空间曲线积分，其中L是圆柱面x2+y2=2y与平面y=z-1的交线，从x轴正向看去取逆时针方向.

问答题讨论函数的连续性．

问答题设X为一个总体且E(X)=k，D(X)=1，X1，X2，…，Xn为来自总体的简单随机样本，令，问n多大时才能使

问答题设(X，Y)的联合概率密度为求：

问答题设(2E-C-1B)=AT=C-1，其中E是4阶单位矩阵，AT是4阶矩阵A的转置矩阵，求A．

问答题设函数f(x)在a≤x≤b上有定义，并且连续，可微．证明：在a＜x＜b上有，其中ξ是a与b之间的某数．

问答题已知向量组有相同的秩，且β3可由α1，α2，α3线性表出，求a，b的值．

问答题已知在(-∞，+∞)上存在原函数，求常数A并求f(x)的原函数。

问答题设，

问答题设f(x)=3x 2 +Ax -3 (x＞0)，A为正常数，问A至少为多少时，f(x)≥20?

问答题设区域D=(x，y)|x2+y2≤1，x≥0，计算二重积分。

问答题71.Vacations were once the prerogative of the privileged few, even as late as the 19th century. Now they are considered the right of all, except for such unfotrunate masses as, for example, the bulk of puplation in certain countries, for whom life, save for sleep and brief periods of rest, is uniterrupted toil. Vacations are more necessary now than before because today the average life is less well-rounded and has become increasingly compartmentalized. 72. I suppose the idea of vacations, as we conceive it, must be incomprehensible to primitive peoples. Rest of some kind has of course always been a part of the rhythm of human life, but earlier ages did not find it necessary to organize it in the way that modern man has done. Holidays and feast days were sufficient. With modern man's increasing tensions, with the stultifying quality of so much of his work, this break in the year's routine became steadily more necessary. 73. Vacations became mandatory for the purpose of renewal and repair. And so it came about that in the United States, the most self-indulgent of nations, the most tense and compartmentalized, vacations have come to take a predominant place in domestic conversation.

问答题求幂级数的收敛区间及和函数，并求级数的和．

问答题若σ有n,个不同特征值，则σ可对角化. 若σ可对角化，则σ有n个不同特征值？