1-2a+a的平方/a-1-根号a的平方-2a+1/a的平方-a
=（a-1)^2/(a-1)-根号（a-1)^2/(a^2-a)
=a-1-(a-1)/(a-1)a
=a-1-1/a
a=1/2+根号3
a-1-1/a
=根号3-1/2-2/(2根号3+1）
=根号3-1/2-2(2根号3-1)/11
=7根号3/11-7/22