观察下列多项式，并进行计算，你能发现什么规律？
(x+1)(x-1) =x2-x+x-1 =x2-1 (m+2)(m-2) =m2-2m+2m-22 =m2-22 =m2-4
(2x+1)(2x-1) =(2x) 2-2x+2x-1 =(2x) 2-1 =4x 2-1
