判别式大于等于0
4m²-4+4m²>=0
m²>=1/2
x1+x2=2m
x1x2=1-m²
x1²+x2²
=(x1+x2)²-2x1x2
=4m²-2+2m²
=6m²-2≥6×1/2-2=1
所以最小值是1