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Sadness isn't manly—this Eric Weaver knew. When depression engulfed this New York police sergeant, it took a different guise: a near-constant state of anger. "One minute I'd be okay and the next minute I'd be screaming at my kids and punching the wall," he recalls. "My kids would ask, 'What's wrong with Daddy? Why's he so mad all the time?'" For years, Weaver didn't know what was wrong. Weaver's confusion about what tortured him was not unusual. Roughly a third of the 18 million or more Americans who suffer depression each year are men. Yet all too often, experts say, men fail to recognize the symptoms and get the treatment they need. For years, experts suspected that gender makes a big difference in depression. Studies from New York to New Zealand have repeatedly found the same startling statistic: About twice as many women as men suffer from depression. That finding was considered one of the bedrock facts of modern mental health. Yet it has recently come under attack from critics who are concerned about underreporting of male depression. William Pollack, Director of the Center for Men at McLean Hospital, is leading the charge against the well-entrenched depression gender gap. He argues that men's rate of depression may be nearly equal to women's. Just look at suicide rates, he says: Male suicides outnumber females four to one. That ratio "is way too high to say that men's depression numbers are so low," he notes. Pollack and others contend that male depression goes unrecognized because, unlike the female version, it often doesn't fit the textbook signs—at least in the early stages. Clinical depression at later stages looks much the same in both sexes. But in the prelude to a breakdown, that deepening despair is often expressed in very different ways. Instead of being weepy, men are more apt to be irritable and angry—moods that aren't included in the classic diagnostic tests. "Their sadness and helplessness are hidden behind a mask of anger," says Pollack. "Men tend to act out" to avoid dealing with uncomfortable feelings, adds Fredric Rabinowitz, a psychologist who works primarily with men. If they feel bad, they're apt to get into fights on the job or at home, withdraw from family and friends, become obsessed with work or hobbies. Most significantly, men often turn to drinking or drugs. Men have two to four times the rate of substance abuse problems as women, and Pollack contends that if this was recognized as a sign of depression, the gender gap would substantially narrow.

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

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As one works with color in a practical, or experimental way, one is impressed by two apparently unrelated facts. Color as seen is a mobile, changeable thing (1) to a large extent on the relationship of the color (2) other colors (3) simultaneously. It is not (4) in its relation to the direct stimulus which (5) it. On the other hand, the properties of surfaces that give (6) to color do not seem to change greatly under a wide variety of illumination color, usually (but not always) looking much the same in artificial light as in daylight. Both of these effects seem to be (7) in large part to the mechanism of color (8) . When the eye is (9) to a colored area, there is an immediate readjustment of the (10) of the eye to color in and around the area (11) . This readjustment does not promptly affect the color seen but usually does affect the next area to which the (12) is shifted. The longer the time of viewing, the higher the (13) , and the larger the area, the greater the effect will be (14) its persistence in the (15) viewing situation. As indicated by the work of Wright and Schouten, it appears that, at (16) for a first approximation, full adaptation takes place over (17) time if the adapting source is moderately bright and the eye has been in (18) darkness just previously. Also, (19) of the persistence of the effect if the eye is shifted around from one object to another, all of which are at similar brightness or have similar colors, the adaptation will tend to become (20) over the whole eye.

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．