6(x+1)^2+2(x-1)(x^2+x+1)-2(x+1)^3=26

6(х+1)2 +2(х-1)(х2+х+1)-2(х+1)3=26
6(х2+2х+1)+2(х3+х2+х-х2-х-1)-2(х3+3х2+3х+1)=26
6х2+12х+6+2(х3-1)-2х3-6х2-6х-2=26
6х2+12х+6+2х3-2-2х3-6х2-6х-2=26
6х=24
Х=4