即x1+x2=-3/2
x1x2=-2
所以x1²+x2²
=(x1+x2)²-2x1x2
=9/4+4
=25/4
(x1-x2)²
=(x1+x2)²-4x1x2
=9/4+8
=41/4
所以x1-x2=±√41/2