7.设总体 sim N(mu ,(sigma )^2) ,X1,X2,···,X9是来自总体X的简单随机样本,X是样本均值,S^2是-|||-样本方差,写出下列抽样分布:-|||-(1) dfrac (3(X-mu ))(sigma ) ;-|||-(2) dfrac (3(overline {X)-mu )}(S) ;-|||-(3) sum _(i=1)^9(({X)_(i)-overline (X))}^2 ;-|||-(4) sum _(i=1)^9(({X)_(i)-mu )}^2-|||-(5) dfrac (9{(x-mu ))^2}({sigma )^2} =-|||-(6) dfrac (9{(overline {X)-mu )}^2}({S)^2} ;-|||-(7) dfrac (2{({X)_(1)-(X)_(2))}^2}({({X)_(3)-(X)_(4))}^2+(({X)_(5)-(X)_(6))}^2} ;-|||-(8) dfrac ({({X)_(1)-(Y)_(1))}^2+(({X)_(2)-(Y)_(1))}^2+(({X)_(3)-(Y)_(1))}^2}({({X)_(6)-(Y)_(2))}^2+( ,其中 _{1)=dfrac ({X)_(1)+(X)_(2)+(X)_(3)}(3) >_(2)=dfrac ({X)_(4)+(X)_(5)+(X)_(6)}(3) -