[latex]64x^6-x^4=x^4(64x^2-1)=x^4\left[(8x)^2-1^2\right]=x^4(8x-1)(8x+1)\\\\\\\\a^2-b^2=(a-b)(a+b)[/latex]

1)x^4(8x-1)^2 =x^4(64x^2-16x+1) =64x^6-16x^5+x^4 2)(8x^3-x^2)^2 =64x^6-16x^5+x^4 3)x^4(8x-1)(8x+1) =x^4(64x^2-1) =64x^6-x^4 4)x^4(64x^2-1) =64x^6-x^4