[题目]设x1,x2,...,x5是总体 approx N(0,1) 的简单-|||-随机样本,则当 k=_ 时, =dfrac (k({x)_(1)+(x)_(2))}(sqrt {{{x)_(3)}^2+({x)_(4)}^2+({x)_(5)}^2}}approx t(3)-|||-__