答：
因为：0a
√[(a-1/a)^2+4]-√[(a+1/a)^2-4]
=√(a^2-2+1/a^2+4)-√(a^2+2+1/a^2-4)
=√(a+1/a)^2 -√(a-1/a)^2
=|a+1/a|-|a-1/a|
=a+1/a-(1/a-a)
=a+1/a-1/a+a
=2a