x²+px+q=x方程根就是x=2
代入q=-2-2p
△=p^2-2p+1-4q=p^2-2p+1+8+8p=0
p^2+6p+9=0
p=-3
q=4
(x-1)²+p（x-1)+q=x+1
x^2-2x+1-3x+3+4-x-1=0
x^2-6x+7=0
△=36-28=8
B={3±根号2}