求微分方程y"一y′+2y=0的通解．

求差分方程y t+1 +2y t =3′的通解．

设f(x)在[0，+∞)上连续，且满足方程求f(t)．

设二阶常系数齐次线性微分方程yˊˊ+byˊ+y=0的每一个解y(x)都在区间(0，+∞)上有界，则实数b的取值范围是 ( )

设y 1 ，y 2 是一阶线性非齐次微分方程y"+p(x)y=q(x)的两个特解，若常数λ，μ使λy 1 +μy 2 是该方程的解，λy 1 一μy 2 是该方程对应的齐次方程的解，则

求微分方程的通解．

求微分方程x 2 y′+xy=y 2 满足初始条件y(1)=1的特解．

微分方程y"一4y=x+2的通解为()．

求微分方程y""+4y"+5y=8cosx的当x→-∞时为有界函数的特解．

求微分方程(y+)dx一xdy=0的满足初始条件y(1)=0的解．

设y=ex为微分方程xy′+P(x)y=x的解，求此微分方程满足初始条件y(ln2)=0的特解．

单选题When Rupert Murdoch sees beams of light in the American advertising market, it is not necessarily time to reach for the sunglasses. Last October, when the impact of September 11th was only beginning to tell, the boss of NASCAR, a media group, had already identified " strong rays of sunshine". With ad sales still languishing, Mr. Murdoch declared last month that " there are some hints of a modest upswing in tile US advertising market". His early optimism turned out to be misplaced. Now, however, other industry observers are beginning to agree with him. Advertising usually exaggerates the economic cycle, falling sharply and early in a downturn, and rebounding strongly once the economy has begun to recover. This is because most managers prefer to trim their ad budgets rather than their payrolls, and restore such spending only once they feel sure that things are looking up. Last year, America's ad market shrank by 9. 8% , according to CMIR, a research firm. Although ad spending has not yet recovered across all media, some analysts now expect overall ad spending to start to grow in the third quarter. The signs of improvement are patchy, however. Ad spending on radio and television seems to be inching up—advertising on American National Radio was up 2% in January on the same period last year, according to Aegis—while spending on magazines and newspapers is still weak. Even within any one market, there are huge differences; just pick up a copy of one of the now-slimline high-teeh magazines that once bulged with ads, and compare it with the hefty celebrity or women's titles. Advertisers in some categories, such as the travel industry, are still reluctant to buy space or airtime, while others, such as the car and movie businesses, have been bolder. The winter Olympics, held last month in Salt Lake City, has also distorted the spending on broadcast advertising in the first quarter. Nonetheless, there is an underlying pattern. One measure is the booking of ad spots for national brands on local television. By early March, according to Mr. Westerfield's analysis, such bookings were growing fast across eight out of the top ten advertising sectors, led by the financial and motor industries. UBS Warburg now expects the " upfront" market, which starts in May when advertisers book advance ad spots on the TV networks for the new season in September, to be up 4% on last year. On some estimates, even online advertising could pick up by the end of the year.

单选题What's your earliest childhood memory? Can you remember learning to walk? Or talk? The first time you heard thunder or watched a television program? Adults seldom (1) events much earlier than the year or so before entering school, (2) children younger than three or four (3) retain any specific, personal experiences. A variety of explanations have been (4) by psychologists for this "childhood amnesia". One argues that the hippo-campus; the region of the brain which is (5) for forming memories, does not mature until about the age of two. But the most popular theory (6) that, since adults don't think like children, they cannot (7) childhood memories. Adults think in words, and their life memories are like stories or (8) one event follows (9) as in a novel or film. But when they search through their mental (10) for early childhood memories to add to this verbal life story, they don't find any that fit the (11) . It's like trying to find a Chinese word in an English dictionary. Now psychologist Annette Simms of the New York State University offers a new (12) for childhood amnesia. She argues that there simply aren't any early childhood memories to (13) . According to Dr. Simms, children need to learn to use someone else's spoken description of their personal (14) in order to turn their own short-term, quickly forgotten (15) of them into long-term memories. In other (16) , children have to talk about their experiences and hear others talk about (17) --Mother talking about the afternoon (18) looking for seashells at the beach or Dad asking them about their day at Ocean Park. Without this (19) reinforcement, says Dr. Simms, children cannot form (20) memories of their personal experiences.Notes: childhood amnesia 儿童失忆症。

单选题Though it is mere 1 to 3 percent of the population, the upper class possesses at least 25 percent of the nation's wealth. This class has two segments: upper-upper and lower-upper. Basically, the upper-upper class is the "old rich"—families that have been wealthy for several generations—an aristocracy of birth and wealth. Their names are in the Social Register, a listing of acceptable members of high society. A few are known across the nation, such as the Rockefellers, Roosevelts, and Vanderbilts. Most are not visible to the general public. They live in grand seclusion, drawing their income from the investment of their inherited wealth. In contrast, the lower-upper class is the "new rich". Although they may be wealthier than some of the old rich; the new rich have hustled to make their money like everybody else beneath their class. Thus their prestige is generally lower than that of the old rich, who have not found it necessary to lift a finger to make their money, and who tend to look down upon the new rich. However its wealth is acquired, the upper class is very, very rich. They have enough money and leisure time to cultivate an interest in the arts and to collect rare books, painting, and sculpture. They generally live in exclusive areas, belong to exclusive social clubs, communicate with each other, and marry their own kind—all of which keeps them so distant from the masses that they have been called the out-of-sight class. More than any other class, they tend to be conscious of being members of a class. They also command an enormous amount of power and influence here and a broad, as they hold many top government positions, run the Council on Foreigh Relations, and control multinational corporations. The actions affect the lives of millions.

问答题Directions:Writeanessayof160—200wordsbasedonthefollowingphoto.Inyouressay,youshould1)describethephotobriefly,2)illustratethegoodofvolunteerworkwith(a)specificexample(s),and3)makeyoursuggestion(s)tofindvolunteerwork.YoushouldwriteitneatlyonANSWERSHEET2.

问答题Practically speaking, the artistic maturing of the cinema was the single-handed achievement of David W. Griffith (1875-1948). (46)Before Griffith, photography in dramatic films consisted of little more than placing the actors before a stationary camera and showing them in full length as they would have appeared on stage. From the beginning of his career as a director, however, Griffith, because of his love of Victorian painting, employed composition. He conceived of the camera image as having a foreground and a rear ground, as well as the middle distance preferred by most directors. By 1910 he was using close-ups to reveal significant details of the scene or of the acting and extreme long shots to achieve a sense of spectacle and distance. His appreciation of the camera' s possibilities produced novel dramatic effects. (47) By splitting an event into fragments and recording each from the most suitable camera position, he could significantly vary the emphasis from camera shot to camera shot. Griffith also achieved dramatic effects by means of creative editing. By juxtaposing images and varying the speed and rhythm of their presentation, he could control tile dramatic intensity of the events as the story progressed. (48) Despite the reluctance of his producers, who feared that the public would not be able to follow a plot that was made up of such juxtaposed images, Griffith persisted, and experimented as well with other elements of cinematic syntax that have become standard ever since. These included the flashback, permitting broad psychological and emotional exploration as well as narrative that was not chronological, and the crosscut between two parallel actions to heighten suspense and excitement. In thus exploiting fully the possibilities of editing, Griffith transposed devices of the Victorian novel to film and gave film mastery of time as well as space. Besides developing the cinema's language, Griffith immensely broadened its range and treatment of subjects. (49) His early output was remarkably eclectic: it included not only the standard comedies, melodramas, westerns, and thrillers, but also such novelties as adaptations from Browning and Tennyson, and treatments of social issues. As his successes mounted, his ambitions grew, and with them the whole of American cinema. When he remade Enoch Arden in 1911, he insisted that a subject of such importance could not be treated in the then conventional length of one reel. Griffith' s introduction of the American-made multi-reel picture began an immense revolution. Two years later, Judith of Bethulia, an elaborate historic philosophical spectacle, reached the unprecedented length of four reels, or one hour' s running time. (50) From our contemporary viewpoint, the pretensions of this film may seem a little ridiculous, but at the time it provoked endless debate and discussion and gave a newintellectual respectability to the cinema.

填空题差分方程y x+1 一y x =x2 x 的通解为___________．

填空题差分方程y t+1 一y t 一2t 2 +1的特解形式为y t * =________．

填空题微分方程+y=1的通解是________．