解
(x+1)(x²+1)(x⁴+1)(x-1)
=(x²-1)(x²+1)(x⁴+1)
=(x⁴-1)(x⁴+1)
=x^8-1
(3+2a-y)(2a+y-3)
=[2a-(y-3)][2a+(y-3)]
=(2a)²-(y-3)²
=4a²-y²+6y-9
x²-y²-4x-4y
=(x-y)(x+y)-4(x+y)
=(x+y)(x-y-4)