概车纶与款理统外 所以当n=2,3,.时， P(X=mY-m =P(X=m.y-n P(Y=n) p2q"-2 1 n-1pg时n-1 当m=1,2,n-1时， PW=iX=mg=PX=Ly=四 P(X=m =pq"-2 pga=pg"m-, n=m+1,m+2,.所以当 n = 2,3,  时, 2 2 2 2 ( 1) − − − = n n n p q p q { } { , } P Y n P X m Y n = = = = , 1 1 − = n 当 m = 1,2,  ,n − 1时, { } { , } P X m P X m Y n = = = = 1 2 2 − − = m n p q p q , − −1 = n m pq n = m + 1,m + 2,  . P{X = mY = n} P{Y = n X = m}