A^3-8b^3 x^2y-36y^3 -5m^2+10mn-5n^2 4ab-28b-8a+56 a^4-81

1) (a-2b)(a^2+2ab+4b^2)
2) y(x^2-36y^2) = y(x-6y)(x+6y)
3) -5(m^2-2mn+n^2) = -5(m-n)^2
4) 4(ab-7b-2a+14) = 4(b*(a-7)-2(a-7)) = 4(b-2)(a-7)
5) (a^2-9)(a^2+9) = (a-3)(a+3)(a^2+9)