点A关于点B的对称点为C,即A和C到B的距离相等,C=B+(B-A)=2√3-1
而x+1/x=x^2+x/x= (12-2√3)/(2√3-1)
=(12-2√3)(2√3+1)/(2√3-1)(2√3+1)
=22√3/11
=2√3