还有一数列道题 麻烦也告诉下思路

设an=x1n+y1, bn=x2n+y2
(x1n+y1)/(x2n+y2)=3n/(2n-3)
2x1n^2-3x1n+2y1n-2y1=3nx2n+3ny2
n(3x2n+y2)=2x1n^2-3x1n+2y1n-2y1

原式=n(3x2n+y2)/[n(x1+y1+x1n+y1)/2]
=(2x1n^2-3x1n+2y1n-2y1)/[n(x1+y1+x1n+y1)/2]
=[4x1n^2-(6x1-4y1)n-4y1]/[x1n^2+(x1+2y1)n]

n趋向于无穷大时，只看最高次项
原式=4x1n^2/x1n^2=4

有点意思

{bn}后面写的什么呢？看不清

来自：求助得到的回答