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=-1-√21/3或x=-1+√21/3