单选题设函数f(x)=2sinx，则f'(x)等于( )．

单选题设α，β是方程(lgx)2+(1+lg5)lgx+lg5=0的两个根，那么αβ=()．

单选题Teach for America (TFA) was founded by Wendy Kopp in 1990. It is a non-profit organisation that recruits top-notch graduates from elite institutions and gets them to teach for two years in struggling state schools in poor areas. I had thought the programme was about getting more high-quality teachers — but that, it appears, is a secondary benefit. “This is about enlisting the energy of our country’s future leaders in its long-term educational needs, and eliminating inequity,” Wendy explains. It’s great if “corps members”, as TFA calls its active teachers, stay in the classroom — and many do, and rise quickly through the ranks. But the “alums”, as she calls those who have finished their two-year teaching, who don’t stay in schools often go on to lead in other fields, meaning that increasing numbers of influential people in all walks of life learn that it is possible to teach successfully in low-income communities, and just what it takes. “It means you realise that we can solve this problem.” As she continues to talk I realise that TFA is — in the best possible sense — a cult. It has its own language (“corps members”, “alums”), recruits are instilled (“We tell them that it can be done, that we know of hundreds, thousands, of teachers attaining tremendous success”), go through an ordeal (“Everyone hits the wall in week three in the classroom”), emerge transformed by privileged knowledge (“Once you know what we know — that kids in poor urban areas can excel — you can accomplish different things”) and can never leave (alumni form a growing, and influential, network). I have not seen the same zeal when talking to those on the equivalent programme in England, Teach First., in which the missionary-style language imported from America had to be toned down, because it just didn’t suit the restrained English style. But could that favour be necessary for its success? Chester, an alum, takes me to visit three TFA corps members at a middle school in the Bronx. They are impressive young people, and their zeal is evident. Two intend to stay in teaching; both want to open charter schools. One, a Hispanic woman, is working out with a friend how to educate migrant Hispanic labourers in Texas; the other would like to open a “green” charter, but in the meantime he has accepted a job with the KIPP charter group in Newark, New Jersey. All three are tired. Their classrooms are not much like the rest of the school where they work, and their heroic efforts are only supported by Chester and each other, not by their co-workers. “The first year was unbelievably bad,” one tells me. “So many years with low expectations meant a lot of resistance from the kids. Eventually they saw the power and the growth they were capable of.”

单选题一个长方体，有公共顶点的三个面的对角线长分别为a，b，c，则它的对角线的长是( )．

单选题 利用平移化简方程 ,并指出它表示何种曲面. A、它表示旋转单叶双曲面 B、, 它表示旋转单叶双曲面 C、它表示旋转单叶双曲面 D、它表示旋转单叶双曲面

单选题设有编号1、2、3、4、5的5个球和编号为1、2、3、4、5的5个盒子。现将这5个球放入这5个盒子内，要求每个盒内放一个球，并且恰好有2个球的编号与盒子的编号相同，则这样的投放方法的总数为( )。 (A)20 (B)30 (C)60 (D)120 (E)136

单选题下列函数在区间[0，3]上不满足拉格朗日定理条件的是______A．f(x)=2x2+x+1B．f(x)=cos(x+1)C．D．f(x)=ln(1+x)

单选题已知x1，x2，x3的算术平均值为a，y1，y2，y3的算术平均值为b，则2x1+3y1，2x2+3y2，2x3+3y3的算术平均值为______．A．2a+3bB．C．6a+9bD．2a+bE．以上结论均不正确

单选题设在区间[a，b]上f(x)＞0，f'(x)＜0，f"(x)＞0，令，S2=f(b)(b-a)，S3=[f(a)+f(b)](b-a)，则______。A.S1＜S2＜S3B.S2＜S1＜S3C.S3＜S1＜S2D.S2＜S3＜S1

单选题设A为n阶矩阵，则下列结论不正确的是

单选题等差数列an中，a1+a7=42，a10-a3=21，则前10项的S10等于______。 A．720 B．257 C．255 D．259