(2х+3)(2х-1)-(2х+1)(2х-1)=
(4х^2-2х +6х-3)-(4х^2 - 2х+2х-1)=
4х^2 - 2х+6х-3-4х^2 +2х-2х+1=
4х-2=2(2х-1)
(2х+3)(2х-1)-(2х+1)(2х-1)=
(4х^2-2х +6х-3)-(4х^2 - 2х+2х-1)=
4х^2 - 2х+6х-3-4х^2 +2х-2х+1=
4х-2=2(2х-1)