4x^2 - 1 - (x^2 + x - 3x - 3) - 18 = 0 

4x^2 - 1 - (x^2 - 2x - 3) - 18 = 0 

4x^2 - 1 - x^2 + 2x + 3 - 18 = 0 

3x^2 + 2x - 16 = 0 

D = 4 + 4*16*3 = 196 = 14^2

x1 = ( - 2 + 14)/6 = 12/6 = 2;

x2 = ( - 2 - 14)/6 = - 16/6 = - 8/3 = - 2 целых 2/3 

раскрываем скобки

4x^2+2x-2x-1-(x^2+x-3x-3)=18

4X^2-1-x^2+2x+3=18

3x^2+2x+2-18=0

дискриминант=4+4*3*16=196=14^2

x1=(-2-14)/6=-8/3

x2=(-2+14)/6=6