1) 14х-12-81=0;
14х=93;
х=93:14;
х=6 цел 9/14;
2) 12с-8-8с-6=0;
4с=14;
с=14:4;
с=3,5;
3) 2х-6+2х+4= 2(3х-х^2+6-2х);
4х-2=2(х-х^2+6); делим на 2;
х^2-х-6+2х-1=0;
х^2+х-7=0;
(х^2+2*1/2х+1/4)-1/4-7=0;
(х+1/2)^2=29/4;
х+1/2=+-(29^1/2)/2;
х1=-1/2-(29^1/2)/2;
х2=-1/2+(29^1/2)/2.