x1^2-x2^2=0,
(x1+x2)(x1-x2)=0,
当x1+x2=0,
-(2m-1)=0,
m=1/2,
当x1=x2,
(2m-1)^2-4m^2=0,
4m^2-4m+1-4m^2=0,
m=1/4