原式=(x+1)²(x-1)²-4(x+1)²
=(x+1)²[(x-1)²-4]
=(x+1)²(x-1+2)(x-1-2)
=(x+1)²(x+1)(x-3)
原式=(x²+x)²-2(x²+x)-3
=(x²+x+1)(x²+x-3)