[a/根号b+b/根号a]-[根号a+根号b]
=[(a根号a+b根号b)/根号(ab)]-[(a根号b+b根号a)/根号(ab)]
=[(a根号a-a根号b)+(b根号b-b根号a)]/根号(ab)
=[a(根号a-根号b)-b(b根号a-b根号b)]/根号(ab)
=(根号a-根号b)(a-b)]/根号(ab)
=(根号a-根号b)(根号a+根号b)(跟号a-根号b)]/根号(ab)
=(根号a-根号b)^2(根号a+根号b)/根号(ab)≥0(而且仅当a=b时划等号)
∴[a/根号b+b/根号a]≥[根号a+根号b] (仅当a=b时划等号)