Question 4275
 (x^6 - y^6)  
  = (x^3 + y^3)(x^3 - y^3)
 then use (x^3 + y^3) = (x+y) (x^2 - xy+^2)
  and (x^3 - y^3) = (x -y) (x^2 + xy+^2)

 Normally, I don't answer such kinds of simple questions,
 but unfortunately, another person gave you incomplete anwser....

 Kenny