(2n+1)^2-(2n-1)^2=(2n+1+2n-1)(2n+1-2n+1)=4n*2=8n, n为正整数PS：式子左边和右边是规律，中间是证明。
3^2-1^2=4*25^2-3^2=4*4 7^2-5^2=4*6（n+1)^2-(n-1)^2=4n （n+1)^2-(n-1)^2=n^2+2n+1-n^2+2n-1=4n
