(X,Y)的联合分布律为 P(X=m, r=n) =P(X=m)P(Y=n X=m) =p(1-p)·p(-p)y p2(1-p) 1,2,…,n-1;n=2,3 1.2∴n=m+1.m+2.2 2 (1 ) − = − n p p = P(X = m)P(Y = n X = m) m =1,2,  ,n −1; n = 2,3,  (m =1,2, ; n = m +1,m + 2, ) (X , Y) 的联合分布律为 1 1 (1 ) (1 ) − − − = −  − m n m p p p p P(X = m,Y = n)