标准正态分布的密度函数是（ ）。A.varphi (x)=dfrac (1)(sqrt {2pi )}(e)^-dfrac ({x^2)(2)}B.varphi (x)=dfrac (1)(sqrt {2pi )}(e)^-dfrac ({x^2)(2)}C.varphi (x)=dfrac (1)(sqrt {2pi )}(e)^-dfrac ({x^2)(2)}D.varphi (x)=dfrac (1)(sqrt {2pi )}(e)^-dfrac ({x^2)(2)}

5、已知随机变量X的密度函数为 (x)=dfrac (1)(2sqrt {2pi )}(e)^-dfrac ({(x-1)^2)(8)}, 则 =dfrac (

某随机变量 X 的概率密度函数为(x)=dfrac (2)(pi )dfrac (1)({e)^x+(e)^-x}，则分布函数为(x)=dfrac (2)(pi

设随机变量X的概率密度为(x)=dfrac (1)(2sqrt {pi )}(e)^-dfrac ({(x-3)^2)(4)}((x)=dfrac (1)(2s

设(X,Y)的分布函数为(x,y)=dfrac (1)({pi )^2}(dfrac (pi )(2)+arctan dfrac (x)(2))(dfrac (

已知氢原子的 (varphi )_(2{p)_(2)}=dfrac (1)(4sqrt {2pi {{a)_(0)}^3}}(dfrac (r)({a)_(0)

. _(Y)(y)=dfrac (1)(2sqrt {2pi )}(e)^-dfrac (y{2)} ,gt 0-|||-bigcirc ._(Y)(y)=d

设(x)=((2-x))^tan dfrac (pi {2)x},(dfrac (1)(2)lt xlt 1),求(x)=((2-x))^tan dfrac (

(int )_(-infty )^+infty (x)^2(e)^-a(x^2)dx=dfrac (1)(2)sqrt (dfrac {pi )({a)^3}}

(19) int tan sqrt (1+{x)^2}cdot dfrac (xdx)(sqrt {1+{x)^2}}-|||-(20) int dfrac (

(19) int tan sqrt (1+{x)^2}cdot dfrac (xdx)(sqrt {1+{x)^2}}-|||-(20) int dfrac (