单选题下列方程为一阶线性微分方程的是______ A. (y')2+2y=x B. y'+2y2=x C. y'+y=x D. y"+y'=x

单选题在下列微分方程中，以y=C1ex+C2cos2x+C3sin2x(C1，C2，C3为任意常数)为通解的是 (A) y'"+y"-4y'-4y=0． (B) y'"+y"+4y'+4y=0． (C) y'"-y"-4y'+4y=0． (D) y'"-y"+4y'-4y=0．

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

单选题下列级数中属于条件收敛的是______A．B．C．D．

单选题下列四个级数中发散的是______A．．B．．C．．D．．

单选题已知二阶线性常系数齐次微分方程的通解是y=C1e-2x+C2e3x，则此方程为______ A.y"-y'+6y=0 B.y"-y'-6y=0 C.y"+y'-6y=0 D.y"+y'+6y=0

单选题具有特解y1=e-x，y2=2xe-x，y3=3ex的三阶常系数齐次线性微分方程是A．．B．．C．．D．．

单选题微分方程y"+4y'-5y=0的通解是______ A.y=C1ex+C2e5x B.y=C1e-x+C2e5x C.y=C1ex+C2e-5x D.y=C1e-x+C2e-5x

单选题以下可以看作某个二阶微分方程的通解的函数是 (A) y=C1x2+C2x+C3． (B) x2+y2=C． (C) y=ln(C1x)+ln(C1sinx)． (D) y=C1sin2x+C2cos2x．

单选题已知微分方程y"-4y'+4y=0，函数C1C2xe2x(C1，C2为任意常数)为______ A．方程的通解． B．方程的特解． C．非方程的解． D．是解，但不是通解也不是特解．

单选题级数(α＞0，β＞0)的敛散性______A．仅与β取值有关．B．仅与α取值有关．C．与α和β的取值有关．D．与α和β的取值无关

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.

单选题微分方程y"-4y=x+2的通解为______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

单选题具有特解y1=e-x，y2=2xe-x，y3=3ex的三阶常系数齐次线性微分方程是 (A) y'"-y"-y'+y=0． (B) y'"+y"-y'-y=0． (C) y'"-6y"+11y'-6y=0． (D) y'"-2y"-y'+2y=0．

单选题如果y=cos2x是微分方程y'+P(x)y=0的一个特解，则该方程满足初始条件y(0)=2的特解为______ A．y=cos2x+2． B．y=cos2x+1． C．y=2cosx． D．y=2cos2x．

单选题微分方程y"+y=x2+2x+cox的特解可设为

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 (A) C1y1+C2y2+y3． (B) C1y1+C2y2+(1-C1-C2)y3． (C) C1y1+C2y2-(C1+C2)y3． (D) C1y1+C2y2-(1-C1-C2)y3．

单选题若在x=-1处收敛，则此级数在x=2处______A．条件收敛．B．绝对收敛．C．发散．D．收敛性不确定．

单选题微分方程y"-3y'+2y=3x-2ex的特解形式为