你题目错了,应该是(n+1)an-n(an+1)=2,不然原式为an-nan+1=2,写起来无意义,除n(n+1)得:an/n-a(n+1)/(n+1)=2/[n/(n+1)]=2[1/n-1/(n+1)]a(n-1)/(n-1)-an/n=2[1/(n-1)-1/n)].....a1/1-a2/2=2(1-1/2),相加得:a1-an/n=2(1-1/n)得an=5n-2