Question 348704
{{{3x^4-81xy^3}}}
{{{3x* (x^3 - 27y^3)}}}  The terms on the right are a difference of 2 cubes
Use this formula to solve
http://www.purplemath.com/modules/specfact2.htm

Here is the solution
http://www.wolframalpha.com/input/?i=3x^4-81xy^3