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.