a-1分之a的平方-1减a的平方-a分之根号a的平方-2a+1
=(a-1)(a+1)/(a-1)-(a-1)²/[a(a-1)]
=a+1-(a-1)/a
=(a²+a-a+1)/a
=(a²+1)/a
=a+1/a
=2-√3+1/(2-√3)
=2-√3+2+√3
=4