当x＝2－根号3分之1时,求代数式x²－4x＋2的值

解
x=1/(2-√3)=(2+√3)/(2-√3)(2+√3)=2+√3
∴
x-2=√3
两边平方得：
(x-2)²=(√3)²=3
∴x²-4x+2
=(x²-4x+4)-2
=(x-2)²-2
=3-2
=1
[(a-1)+2/(a+1)]÷(a²+1)——这个吗?
=[(a-1)(a+1)/(a+1)+2/(a+1)]÷(a²+1)
=(a²-1+2)/(a+1)×1/(a²+1)
=1/(a+1)
=1/(√2-1+1)
=1/√2
=√2/2