7.设X1,X2,···,X6是来自总体 sim N(0,1) 的简单随机样本.-|||-(1)当 k= __ _时, =dfrac (k({X)_(1)+(X)_(2)+(X)_(3))}(sqrt {{{X)_(3)}^2+({X)_(4)}^2+({X)_(5)}^2}}sim t(3) --|||-(2)当 C= __ _时, =dfrac (C({{X)_(1)}^2+({X)_(2)}^2)}(sqrt {{{X)_(3)}^2+({X)_(4)}^2+({X)_(5)}^2+({X)_(6)}^2}}sim F(2,