(2n^2-1)-(2(n-1)^2-1)=4n-2 ..
问题描述：
(2n^2-1)-(2(n-1)^2-1)=4n-2 ..
答
都展开,左边变成2n^2-1-2(n^2-2n+1)+1=2n^2-1-2n^2+4n-2+1=4n-2
(2n^2-1)-(2(n-1)^2-1)=4n-2 ..
都展开,左边变成2n^2-1-2(n^2-2n+1)+1=2n^2-1-2n^2+4n-2+1=4n-2