1. x^2-16-ax+4a=(x-4)(x+4)-a(x-4)=(x-4)(x+4-a)
2. x^2+6x+5=(x+5)(x+1)
3. x^6+64= (x^2)^3+4^3=(x^2+4)(x^4-4x^2+16)=(x^2+4)((x^4+8x^2+16)-12x^2)= (x^2+4)((x^2+4)^2-(2x√3)^2)=(x^2+4)(x^2+4-2x√3)(x^2+4+2x√3)
4. (a+x)^2-2x-2a=(x+a)^2 - 2(x+a)=(x+a)(x+a-2)