18.(导选题,5,0分)-|||-在下列无穷级数中,收敛的级数是 ()-|||-A sum _(n=1)^infty (sqrt (n+1)-sqrt (n));-|||-B sum _(n=1)^infty ((dfrac {n)(n+1))}^n-|||-sum _(n=1)^infty ln (1+dfrac (1)(n));-|||-D sum _(n=1)^infty dfrac ({(-1))^n-1}({n)^2+1}.

函数y=lnx+(1)/(x)，当x=3时，导数为（ ）A. (1)/(3)B. (2)/(9)C. (3)/(4)D. (2)/(5)

设有随机变量X，Y，Z,已知EX=1, EY=2,EZ=-1,DX=1,DY=2,DZ=3,且rho xY=0,, rho xz=dfrac (1)(2), rho yz=-dfrac (1)(2),分别求D(X+Y+Z)和rho xY=0,, rho xz=dfrac (1)(2), rho yz=-dfrac (1)(2),

36.(单选题)（两个重要极限036）lim_(xtoinfty)(1-(2)/(x))^3x=( )A. e^-2B. e^-3C. e^-6D. e^-9

设幂级数sum _(n=1)^infty (a)_(n)((x-2))^n在sum _(n=1)^infty (a)_(n)((x-2))^n处收敛，则此幂级数在sum _(n=1)^infty (a)_(n)((x-2))^n处( ).A.一定发散 B.一定条件收敛C.一定绝对收敛 D.敛散性不能判定

6.(单选题)(三角函数基础118)已知 sin alpha -3cos alpha =0 且α是第三象限角,则 sin alpha -cos alpha 的值为() ()-|||-A dfrac (4sqrt {10)}(5)-|||-B dfrac (4sqrt {10)}(5)-|||-C dfrac (sqrt {10)}(5)-|||-D dfrac (sqrt {10)}(5)

下列各向量组中线性相关的有（ ）。（A）1 -1-|||-x1= 2 α2= 1（B）1 -1-|||-x1= 2 α2= 1（C）1 -1-|||-x1= 2 α2= 1（D）1 -1-|||-x1= 2 α2= 1

【题目】-|||-(11) lim sqrt [n]({2)^n+(3)^n+(4)^n}= __-|||-(12)设 lim _(xarrow -1)dfrac ({x)^3+a(x)^2+x+2}(x+1)=b(k 为有限数),则 a+b= __ _-|||-(13) lim _(xarrow infty )(xsin dfrac (1)(x)+dfrac (1)(x)sin x)= __-|||-(14) lim _(xarrow 0)(xsin dfrac (1)(x)+dfrac (1)(x)sin x)= __ -.-|||-(15)设 lim _(xarrow infty )((dfrac {x+2a)(x-1))}^x=(e)^3 ,则 a= __-|||-(16) lim sqrt [x](1-2x)= __ _.-|||-(17)已知 (x)=2x+4sin x sin x f(x) 则 f(x)= __ --|||-(18)已知 f(x)= { , xlt 0 b, x=0 a+cos x, xgt 0 的连续区间为 __

6. (int )_(0)^a(e)^3xdx=dfrac (1)(3)(e-1), 则a= () 。-|||-A. dfrac (1)(2) B.dfrac (1)(3) c.dfrac (1)(4) D.1

三、(本大题8分)计算4阶行列式的值-|||-D= |} 3& 1& -1& 2 -5& 1& 3& -4 2& 0& 1& -1 1& -5& 3& -3 | .-|||-5 1 .-1-|||- 1 -1 0 0 =(-1) 3+3 -11 1 -1 |=(-1)^(1+3)| -6 2| =40.······(2分)-|||-5 1 1-|||-解: D= -11 1 3-|||-0 0 1 -5 -5-|||--5 -5 3-|||--5 -5 0-|||-(2分) ......(2分) ······(2分)

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