+(x)_(n))}^2+b(({x)_(n+1)+... +(x)_(n))}^2-|||-(1)求a,b的值使得Y服从x^2分布;-|||-(2)求c,d的值,使 =dfrac (c({X)_(1)+(X)_(2)+... +(X)_(m))}(dsqrt {{{X)_(min+1)}+... +({X)_(n)}}^2} 服从t分布.