（X^2-2X+1)-(2X^2-2)=0X^2-2X+1-2X^2+2=0-X^2-2X+3=0-(X^2+2X-3)=0-(X-1)(X+3)=0x1=1,x2=-3
把x^2-1拆成（x-1)*(x+1)两边同时约去一个（x-1)就变成了x-1-2(x-1)=0 ,x=-3
