(1)原式=x²-9²=(x+9)(x-9)
(2)原式=[(1/2)a]²-b²=[(1/2)a+b][(1/2)a-b]
(3)原式=[3(x-y)]²-5²=[3(x-y)+5][3(x-y)-5]
(4)原式=(x²-y)²-[2(y-1)]²=[x²-y+2(y-1)][x²-y+2(y-1)]
(5)原式=(x²)²-9²=(x²+9)(x²-3²)=(x²+9)(x+3)(x-3)
(6)原式=[(3x)³]²-(3x)²=(27x³+3x)(27x³-3x)
(7)原式=(a²-2b+1-2b)(a²-2b-1+2b)=(a²+1-4b)(a²-1)=(a²+1-4b)(a+1)(a-1)
(8)原式=[(3x)²]²-(6y)²=(9x²+6y)(9x²-6y)=[3(3x²+2y)][3(3x²-2y)]