单选题已知y1=xex+e2x，y2=xex+e-x是二阶非齐次线性微分方程的解，则此方程为

单选题设y1(x)，y2(x)，y3(x)是二阶线性非齐次微分方程y"+p(x)y'+q(x)y=f(x)的三个线性无关解，C1，C2是任意常数，则此微分方程的通解是

单选题微分方程的一个特解应具有形式(式中α，b为常数)

单选题级数(a为常数)______A．绝对收敛．B．条件收敛．C．发散．D．敛散性与a有关．

单选题设φ1(x)，φ2(x)，φ3(x)为二阶非齐次线性方程y"+a1(x)y'+a2(x)y=f(x)的三个线性无关的解，则该方程的通解为______ A．C1[φ1(x)+φ2(x)]+C2φ3(x)． B．C1[φ1(x)-φ2(x)]+C2φ3(x)． C．C1[φ1(x)+φ2(x)]+C2[φ1(x)-φ3(x)]． D．C1φ1(x)+C2φ2(x)+C3φ3(x)，其中C1+C2+C3=1．

单选题微分方程y"=y'的通解为______ A. y=C1+C2e2x B. y=C1+C2ex C. y=C1+C2x D. y=C1x+C2x2

单选题设为正项级数，下列结论中正确的是______A．若=0，则级数收敛．B．若存在非零常数λ，使得，则级数发散．C．若级数收敛，则=0．D．若级数发散，则存在非零常数λ，使得．

单选题设a，b，c为待定常数，则微分方程y"-3y'+2y=3x-2ex的特解形式为______ A．(ax+b)ex． B．(ax+b)xex． C．(ax+b)+cex． D．(ax+b)+cxex．

单选题设an＞0(n=1，2，3，…)且收敛，常数λ∈(0，)，则级数______A．绝对收敛．B．条件收敛．C．发散．D．敛散性与A有关．

单选题若级数收敛，则级数______A．收敛．B．收敛．C．收敛．D．收敛．

单选题Walt Disney could have built his biggest theme park anywhere. He chose Florida. The weather is balmy, and when it gets too hot there are lots of pools to cool off in, says. Meg Crofton, Walt Disney World's CEO'. Florida also offers plenty of space to expand. Disney World, which was first carved out of wild woodland in 1971, has swollen to four parks covering 40 square miles ( 104 sq km) and employing 60 000 "cast members". Contrary to the stereotype of rapid flow in the service sector, the average full-time employee sticks around for nine years. Florida's business climate is sunny, too. The Milken Institute, a think-tank in California, compiles an index of "best-performing cities" in America, a composite measure of such things as job creation, wage growth and whether businesses are thriving. In the most recent index, six of the top ten metropolitan areas are in Florida. ( Orlando-Kissimmee is sixth. ) And 18 of the top 30 are in the South. For a long time the South's weather got in the way of its development. Richard Pillsbury, a geography professor at Georgia State University, describes traditional life in the lowland South, a region stretching from northern Virginia down to the Gulf coast of Texas: "Smallish barren farms almost lost in the white heat of a hot and humid summer sun as the owners and their help fought swarms of mosquitoes to plant, cultivate and harvest the meagre cotton crop for market." Then air-conditioning came. As it spread after the World War Ⅱ, the South became suddenly more comfortable to live and work in. From the 1940s until the 1980s the region boomed. In his book Old South, New South, Gavin Wright lists four reasons why Federal defence spending stimulated growth. Sunshine attracted skilled professionals. The South, having developed so little in the past, was a "clean slate", without strong labour unions, entrenched bureaucracies, restrictive laws or outdated machinery. Lastly, given how much catching up the South had to do, the potential returns were higher than in the north. Southerners have prospered in part by playing to their traditional strengths. The fame of southern hospitality has bolstered the region's hotel chains, such as Holiday Inn. That of southern cuisine helps local restaurants, such as Waffle House, Cracker Barrel and KFC. Arkansas-based Wal-Mart, the world's largest retailer, has kept costs low by refusing to recognize unions. And Coca-Cola owes at least some of its success to its southern origins.

单选题微分方程y"+2y'+y=(x+1)e-x+2x+1有一个特解y*形式为 (A) y*=x(ax+b)e-x+(cx+d)． (B) y*=(ax+b)e-x+x2(cx+d)． (C) y*=x2(ax+b)e-x+(cx+d)． (D) y*=(ax+b)e-x+x(cx+d)．

单选题若y=xex+x是方程y"-2y'+ay=bx+c的解，则

单选题下列结论不正确的是

单选题微分方程y"-3y'+2y=3x-2ex的特解形式为 (A) (ax+b)ex． (B) (ax+b)xex． (C) (ax+b)+cex． (D) (ax+b)+cxex．

单选题若A，B为非零常数，c1，c2为任意常数，则微分方程y"+k2y=cosx的通解应具有形式 (A) c1coskx+c2sinkx+Asinx+Bcosx． (B) c1coskx+c2sinkx+Axsinx． (C) c1coskx+c2sinkx+Axcosx． (D) c1coskx+c2sinkx+Axsinx+Bxcosx．

单选题微分方程y"+2y'+y=3xe-x的特解形式为

单选题函数y=C1ex+C2e-2x+xex满足的一个微分方程是A．．B．．C．．D．．

单选题When the United States and Korea(SOK) announced their new free-trade agreement last month, the news was mainly economic. The deal would give American farmers and bankers alike better access to Korean consumers and help Korean companies push more electronics, cars and textiles into the United States. Largely unreported was the political angle--the U.S.-Korea(SOK) free trade agreement comes at precisely the moment when America's military presence on the Korean Peninsula is rapidly diminishing, anti-U.S. nationalism in Korea(SOK) is growing and China is playing an ever more important leadership role in the region. This FTA is much more significant in strategic than economic terms. It is the same about any number of trade deals in Asia these days. While free-trade agreements have always been somewhat political, solidifying national relationships, the use of FTAs in geopolitical jockeying(竞赛) is reaching new heights in East Asia. Since 1997, the number of FTAs in the region has risen from seven to 38. Last time we saw this sort of frenzied bilateral activity was back in the 1930s. That worries some economists, who fear that all the free-trade politicking will further erode an already beleaguered global trading system, and create a snowball effect of countermeasures. It's no accident that the activity in the region has increased since 2004, which marked the beginning of a massive free trade agreement between China and the Association of Southeast Asian Nations. China offered countries like Laos and Cambodia an "early harvest," unilaterally opening up markets for hundreds of different kinds of agricultural products. That in turn helped smooth the way for a reduction in tension in hot spots like the disputed South China Sea territories. FTAs are becoming a key instrument for great-power diplomacy. That worries rivals, who are rushing to find their own partners. The Japanese, for example, have always been cautious when it comes to bilateral agreements. Japanese Prime Minister Shinzo Abe recently announced a new push for more Japanese FTAs in the region. Meanwhile, the EU is trying desperately to push its way back into the region, recently announcing plans to negotiate its own deals with both South Korea and the ASEAN nations. How will all the wheeling and dealing end? Not with more efficient trading. A recent map of Asian trade deals shows an increasingly complicated "spaghetti bowl" hindering broader global efforts to liberalize trade. Such deals have a disproportionately negative effect on small and medium-sized enterprises, representing as much as 80 percent of jobs in some parts of Asia. Already, the U.S.-Korea(SOK) deal is causing grousing(不满) in Japan, which would take a hit as Korean competitors no longer have. to deal with U.S. tariffs. Still, that probably won't turn the tide -- the most important criterion in motivating a country to seek FTAs, well ahead of economic reform, was--surprise --politics.

单选题微分方程y'+xy=0的通解是______A．B．C．D．y=(其中C为任意常数)