设 s= ‘Happy New Year’,则s[3:8]的值为 （）

The ____________ on this apartment expiresin a year’s time.

A) treaty B)lease

C) engagement D) subsidy

In this age of Internet chat, videogames and reality television, there is no shortage of mindless activities to keep a child occupied. Yet, despite the competition, my 8-year-old daughter Rebecca wants to spend her leisure time writing short stories. She wants to enter one of her stories into a writing contest, a competition she won last yes.

As a writer I know about winning contest, and about losing them. I know what it is like to work hard on a story only to receive a rejection slip from the publisher. I also know the pressures of trying to live up to a reputation created by previous victories. What if she doesn’t win the contest again？ That’s the strange thing about being a parent. So many of our own past scars and dashed hopes can surface.

Why did Rebecca want to enter this year’s writing contest？

A) She believed she possessed real talent for writing.

B) She was sure of winning with her mother’s help.

C) She wanted to share her stories with readers.

D) She had won a prize in the previous contest.

设是群，求出元素a,b∈S,能使

设试用表达Ψ^S(x).

设级数

求:

(1)S(x)所满足的一阶微分方程;(II)S(x)的表达式.

设s是非空有上界的数集,.证明在数集s中可取出严格单调增加的数列{x_n},使得.

设R是实数集,令X=R^{0.1｝，若试证:S是一个偏序.S是全序吗？

设f(P)为二阶连续可微分且可用曲面连通的向量场,S为光滑封闭曲面.

证明:

设单位反馈系统的开环传递函数为

当输入信号x(t)为5rad/s的正弦信号时，求系统稳态误差。