﹙1﹚x²-9
=x²-3²
=(x+3)(x-3)
﹙2﹚a²-4/25b²
=a²-(2/5b)²
=(a+2/5b)(a-2/5b)
﹙3﹚16x²-4y²
=4(4x²-y²)
=4(2x+y)(2x-y)
﹙4﹚9a²b²-81a²
=9a²(b²-9)
=9a²(b+3)(b-3)
﹙5﹚6a²b-54b
=6b(a²-9)
=6b(a+3)(a-3)
﹙6﹚x⁴-81y⁴
=(x²)²-(9y²)²
=(x²+9y²)(x²-9y²)
=(x²+9y²)(x+3y)(x-3y)
﹙7﹚﹙2a+b﹚²-﹙2a-b﹚²
=[(2a+b)+(2a-b)][(2a+b)-(2a-b)]
=4a×2b
=8ab
﹙8﹚9﹙x-2y﹚³-﹙x-2y﹚
=(x-2y)[9(x-2y)²-1]
=(x-2y)[3(x-2y)+1][3(x-2y)-1]
=(x-2y)(3x-6y+1)(3x-6y-1)