题目[题目]设二维随机变量(X,Y)的概率密度为-|||-f(x,y)= ) 2-x-y,0lt xlt 1,0lt ylt 1 0 .-|||-(1)求 (Xgt 2Y) ;-|||-(2)求 =x+y 的概率密度fz(Z).题目解答答案[""]