原式=(x³-x)-(2x-2)
=x(x²-1)-2(x-1)
=x(x+1)(x-1)-2(x-1)
=(x-1)[x(x+1)-2]
=(x-1)(x²+x-2)
=(x-1)(x+2)(x-1)
=(x-1)²(x+2)