Factor completely with respect to the integers.

I just need to see if I can simplify or factor the answers I got even further.

1. x^3 + 64
Answer: (x+4)(x^2-4x+16)
Can this simplify any?

2. 8x^3 - 64
Answer 8(x-2)(x^2+2x+4)

3. x^-2x^2+4x-8
Answer: (x^2+4)(x-2)

4. 2x^3 + 3x^2 - 32x - 48
Answer: (x^2-16)(2x+3)

5. 6x^3-18x^2-2x+6
Answer: (6x^2-2)(x-3)

6. x^4 + 12x^3 + 4x^2 + 48x
Answer:(x^3+4x)(x+12)

They look good to me. The first cannot be simplified.