3x^2-4x-2=0
3(x^2-4x/3)-2=0
3(x^2-4x/3+4/9-4/9)-2=0
3(x-2/3)^2-4/3-2=0
3(x-2/3)^2=10/3
x-2/3=±√10/3
x=(2±√10)/3