当X=m(m=12,…)时,Y的条件分布 律为 P(r=nX=m)= P(X=m,Y=n) P(X=m) b(1-p)2 =p(1-p) n-m-1 p(1-p) n=m+1,m+2,( ) ( , ) P X m P X m Y n = = = = 1 1 2 2 (1 ) (1 ) (1 ) − − −− = − −− = n m mn p p p p p pn = m +1,m + 2, P(Y = n X = m) 律为当 X = m ( m = 1 , 2 ,  ) 时, Y 的条件分布