a/b-b/a=(a²-b²)/ab=[(a+b)(a-b)]÷ab,∵a=2+√3,b=2-√3,∴[(a+b)(a-b)]÷ab=[﹙2+√3+2-√3﹚×﹙2+√3-2+√3﹚]÷﹙2+√3﹚×﹙2-√3﹚=8√3
