x1+x2=2(m-1/2)
x1x2=m^2-2
x1^2-x1x2+x2^2=(x1+x2)^2-3x1x2=4(m-1/2)^2-3(m^2-2)=12
整理得m^2-4m-5=0
m1=-5 m2=1舍