x³-2x²-x+7=5
x³-2x²-x+2=0
(x³-2x²+x)-(2x-2)=0
x(x²-2x+1)-2(x-1)=0
x(x-1)²-2(x-1)=0
(x-1)[x(x-1)-2]=0
(x-1)(x²-x-2)=0
(x-1)(x+1)(x-2)=0
x-1=0 或 x+1=0 或 x-2=0
x1=1,x2=-1,x3=2