题目错了吧……
a+1/a=√10 吧……,
如果是这样
(a-1/a)²
=a²-2＋1/a²
=a²+2+1/a²-4
=a²+2a×1/a+1/a²-4
=（a+1/a)²-4
=10-4
=6
∴a-1/a=正负√6