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问题 填空题

微分方程y’+y=e-xcosx满足条件y(0)=0的解为y=______．

答案

参考答案：e-xsinx

解析：

[分析]： 本题是一阶线性微分方程初值问题求特解．将方程两端同乘积分因子μ(x)=ex即得(yex)’=cosx，两边求积分就有
[*]
移项得所求的特解为y=e-xsinx．
注意，本题也可先求出方程的通解，然后用初值确定其中的任意常数得到解．

选择题

Good food, good sleep, no exercise. That's ________ he gained weight.

A．how

B．when

C．what

D．whether
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单项选择题

A narrowing of your work interests is implied in almost any transition from a study environment to managerial or professional work. In the humanities and social sciences you will at best reuse only a fraction of the material (1) in three or four years’ study. In most career paths academic knowledge only (2) a background to much more applied decision-making. Even with a " training " form of degree, (3) a few of the procedures or methods (4) in your studies are likely to be continuously relevant in your work. Partly this (5) the greater specialization of most work tasks compared (6) studying. Many graduates are not (7) with the variety involved in (8) from degree study in at least four or five subjects a year to very standardized job (9) . Academic work values (10) inventiveness, originality, and the cultivation of self-realization and self-development. Emphasis is placed (11) generating new ideas and knowledge, assembling (12) information to make a " rational " decision, appreciating basic (13) and theories, and getting involved in fundamental controversies and debates. The humanistic values of higher (14) encourages the feeling of being (15) in a process with a self-developmental rhythm. (16) , even if your employers pursue enlightened personnel development (17) and invest heavily in " human capital " —for example, by rotating graduate trainees to (18) their work experiences—you are still likely to notice and feel (19) about some major restrictions of your (20) and activities compared with a study environment.

（7）（）

A.contest

B.content

C.contact

D.contract
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