8x^3 -27y^3 +z^3 -18xyz factorise
Sorry, but this expression doesn't factorise fully,
The best you can do is to take a common factor of x, y or z from the last term, 18xyz, and match it with one of the other three terms.
8x^3 -27y^3 +z^3 -18xyz -> 2x(4x^2 - 9yz) - 27y^3 + z^3
8x^3 -27y^3 +z^3 -18xyz -> 9y(-3y^2 - 2xz) + 8x^3 + z^3
8x^3 -27y^3 +z^3 -18xyz -> z(z^2 - 18xy) + 8x^3 - 27y^3