$\displaystyle x^3 + x^2 - 8y^3 - 4y^2$

i tried doing

$\displaystyle =[x + (-2y)]^3 + x^2 - 4y^2

=[x + (-2y)][(x)^2 - (x)(-2y) + (-2y)^2) + x^2 - 4y^2$

$\displaystyle = [x + (-2y)][(x)^2 -(x)(-2y) + (-2y)^2]$

but I'm pretty sure thats not right...