(x-1)^2 -7(x-1)-8=0

(x-1)^2 -7(x-1)-8=0
把x-1当作一个整体
=>(x-1-8)(x-1+1)=0
=>(x-9)x=0
=> x=0或x=9

(x-1)^2 -7(x-1)-8=0
把（x-1)看成一个整体
[(x-1)-8][(x-1)+1]=0
x(x-9)=0
x=0
x=9

(x-1)^2 -7(x-1)-8=0
[(x-1)-8][(x-1)+1]=0
所以x-1=8或x-1=-1
x=9或x=0

换元，令x-1=a
a^2-7a-8=0
（a-8）（a+1）=0
a=8或a=-1
则 x-1=8 x1=9
x-1=-1 x2=0