(1）9a^3b^3-ab
=ab(9a²b²-1)
=ab(3ab+1)(3ab-1)
（2）mx^2-8mx+16m
=m(x²-8x+16)
=m(x-4)²
（3）-x^4+256
=-(x^4-16²)
=-(x²+16)(x²-16)
=-(x²+16)(x+4)(x-4)
（4）-a+2a^2-a^3
=-a(a²-2a+1)
=-a(a-1)²
（5）27x^2y^-18x^2y+32x^2 这题打错了吧,
应该是:
27x^2y^2-18x^2y+3x^2
=3x²(9y²-6y+1)
=x²(3y-1)²