∵3x^2-9x-1=0的两个根是 x1和x2,∴x1+x2=3,x1x2=-1/3x1x2²+x1²x2=x1x2(x2+x1)=(-1/3)×3=-1|x1-x2|=√(x1-x2)²=√[(x1+x2)²-4x1x2]=√[3²-4×(-1/3)]=√[9+(4/3)]=√(39/4)=½√39...