3x^2+6x-4=0
x^2+2x-4/3=0
x^2+2x+1-1-4/3=0
(x+1)^2-7/3=0
(x+1)^2-21/9=0
(x+1-√21/3)(x+1+√21/3)=0
x=√21/3-1或x=-√21/3-1