Factorise: x7y + xy7
xy(x2-y2)(x4-y4+x2y2)
xy(x2+y2)(x4+y4-x2y2)
xy(x2-y2)(x4+y4-x2y2)
xy(x2+y2)(x4-y2+x2y2)
Factorise: 27x3+y3+z3−9xyz