(B) ({S)_(x)}^2+({S)_(Y)}^2sim ({x)_(x)}^2(2n-2).-|||-(C) dfrac (overrightarrow {X)-overrightarrow (Y)}(sqrt {{{S)_(x)}^2+({S)_(y)}^2}}sim t(2n-2). (D) dfrac ({S)_(x)}^2sim F(n-1,n-1).

(B) (n-1)(S)^2+(overline {X)}^2 (C) (S)^2+(overline {X)}^2. (D) dfrac (n-1)(n)(S

(D) ({x)_(1)}^2+({x)_(2)}^2sim (x)^2((n)_(2)+(n)_(1)-1)

dfrac (dy)(dx)=(x)^2+(y)^2 B . dfrac (dy)(dx)=(x)^2+(y)^2 C .dfrac (dy)(dx)=(x)^

A)(S^2)/(sigma^2) sim chi^2(n-1) B)(n(overline(X)-mu)^2)/(S^2) sim F(1, n-1)

旋转抛物面=dfrac ({x)^2+(y)^2}(2)在=dfrac ({x)^2+(y)^2}(2)那部分的曲面面积S=( )旋转抛物面在那部分的曲面

7-14 设 sim N(2,9), X1,X2,···,Nn为X的样本,则 dfrac (overrightarrow {X)-2}(3/sqrt {n)}-

,(x)_(n),(x)_(n+1) 是来自N(μ,σ^2)的样本, overrightarrow ({x)_(n)}=dfrac (1)(n)sum _(i=

求旋转曲面=(x)^2+(y)^2在点=(x)^2+(y)^2处的法线方程A.=(x)^2+(y)^2B.=(x)^2+(y)^2C.=(x)^2+(y)^2D

( A ) = (x,y,z)|{x)^2+(y)^2+(z)^2=(a)^2,zgeqslant 0} ( B ) = (x,y,z)|{x)^2+(y)^

求函数 (x,y)=x(e)^-dfrac ({x^2+{y)^2}(2)} 的极值.