（x-1）^2-7(x-1)-8=0
(x-1)^2-2x7/2(x-1)+(7/2)^2-8-(7/2)^2=0
(x-1-7/2)^2=8+49/4
(x-9/2)^2=81/4
x-9/2=±9/2
x=0或x=9