令a=√2
x³-2ax²+2x-a+1=0
x(x²-2ax+1)+x-a+1=0
x(x-a+1)(x-a-1)+(x-a+1)=0
(x-a+1)[x(x-a-1)+1]=0
(x-a+1)[x²-(a+1)x+1]=0
x1=a-1=√2-1
x2,3=[(a+1)± √[(a+1)^2-4]]/2=[√2+1± √(2√2-1)]/2