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)

单选题设a＞0为常数，则为______A．绝对收敛．B．条件发散．C．发散．D．收敛性与a有关．

单选题微分方程的特解形式可设为

单选题微分方程①=(x-y)(x+y)，②=cosy+x，③y2dx-(y2+2xy-y)dy=0中，属于一阶线性微分方程的是______A．①．B．②．C．③．D．①②③均不是．

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 (A) y"-y'-2y=ex-2xex． (B) y"+y'+2y=ex-2xex． (C) y"-y'-2y=-ex+2xex． (D) y"+y'+2y=-ex+2xex．

单选题若级数收敛，发散，则______A．必发散．B．必收敛．C．必发散．D．必发散．

单选题下列结论不正确的是(A)若已知y'=P(x)+Q(x)y+R(x)y2的一个特解，则必定可将该方程化为伯努利方程．(B)若微分方程P(x，y)dx+Q(x，y)dy=0有积分因子μ(x，y)，则μ(x，y)必定满足(C)若函数是微分方程y'+y2=0的解，则y=Cy1也是该方程的解．(D)方程y"-y'2+2y=0的任何积分曲线在下半平面内不能有拐点．

单选题微分方程y"=y的通解是______ A. y=C1+C2ex B. y=ex+e-x C. y=C1ex+C2e-x D. y=Cex+Ce-x(其中C，C1，C2为任意常数)

单选题方程y"'+2y"=x2+xe-2x的特解形式为______． A．y=ax2+bx+c+x(dx+e)e-2x． B．y=x2(ax2+bx+c)+x2e-2x． C．y=(ax2+bx+c)+(dx+e)e-2x． D．y=x2(ax2+bx+c)+x(dx+e)e-2x．

单选题已知二阶线性常系数齐次微分方程的两个特解是y1=1与y2=e2x，则此方程为______ A.y"-2y'=0 B.y"+2y'=0 C.y"-3y'+2y=0 D.y"+3y'+2y=0

单选题设有两个数列an，bn，若=0，则______A．当收敛时，收敛．B．当发散时，发散．C．当收敛时，收敛．D．当发散时，发散．

单选题设级数收敛，则必收敛的级数为______A．．B．．C．．D．．

单选题设y1(x)，y2(x)为二阶常系数齐次线性方程y"+py'+qy=0的两个特解，则c1y1(x)+c2y2(x)(c1，c2为任意常数)是该方程通解的充分必要条件是 (A) y1(x)y'2(x)-y2(x)y'1(x)=0． (B) y1(x)y'2(x)-y2(x)y'1(x)≠0． (C) y1(x)y'2(x)+y2(x)y'1(x)=0． (D) y1(x)y'2(x)+y2(x)y'1(x)≠0．

单选题微分方程ylnxdx=xlnydy满足初始条件y|x=1=1的特解是______ A.ln2x+ln2y=0 B.ln2x+ln2y=1 C.ln2x-ln2y=0 D.ln2x-ln2y=1

单选题设y=y(x)是二阶线性常系数非齐次微分方程y"+Py'+Qy=3e2x满足初始条件y(0)=y'(0)=0的特解，则极限=______A．．B．．C．．D．．

单选题微分方程y"+2y'+y=3xe-x的特解形式为 (A) axe-x． (B) (ax+b)e-x． (C) (ax+b)xe-x． (D) (ax+b)x2e-x．

单选题下列方程为一阶线性微分方程的是______ A.y'+xy3=x B.xy'+y=x3 C.y·y'+xy=sinx D.y"+5y'-6y=xe-x

单选题对于微分方程y"+4y'+4y=e-2x，利用待定系数法求其特解y*时，下列特解设法正确的是______ A.y*=Ae-2x B.y*=(Ax+B)e-2x C.y*=Axe-2x D.y*=Ax2e-2x

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