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