2x^3+3x^2-1=0
2x^3+2x^2+x^2-1=0
2x^2(x+1)+(x-1)(x+1)=0
(x+1)(2x^2+x-1)=0
(x+1)(x+1)(2x-1)=0
所以x1=x2=1,x3=1/2.