△=m^2-4(m-2)=m^2-4m+8=(m-2)^2+4>0x1+x2=-mx1x2=m-2|x2-x1|=2√5（x2-x1)^2=20(x1+x2)^2-4x1x2=20m^2-4(m-2)=20m^2-4m-12=0(m-6)(m+2)=0m1=6m2=-2
两根之和为-m,两根之积为m-2d=(m^2-4(m-2))^2=2根号5得m=6或-2
