3*k-81*k^4=3*k * (1-27*k^3) =
3*k * (1-3*k) * (1+9*k+9*k^2)
a^5*b-a^3*b^3-a^2*b^4+b^6=
a^2*b (a^3-b^3) - b^3 * (a^3-b^3) =
b * (a^2-b^2) * (a^3-b^3) =
b * (a+b) * (a-b) ^2 * (a^2+a*b+b^2)
3*k-81*k^4=3*k * (1-27*k^3) =
3*k * (1-3*k) * (1+9*k+9*k^2)
a^5*b-a^3*b^3-a^2*b^4+b^6=
a^2*b (a^3-b^3) - b^3 * (a^3-b^3) =
b * (a^2-b^2) * (a^3-b^3) =
b * (a+b) * (a-b) ^2 * (a^2+a*b+b^2)