8b^3-a^3+a-2b

_________________

1-(a+b)^2-3b^2

8b^3-a^3+a-2b              (2b-a)(4b^2+2ab+a^2)-(2b-a)

_________________ =  __________________________ =

1-(a+b)^2-3b^2               1-a^2-b^2-3b^2

=  (2b-a)(4b^2+2ab+a^2-1)

___________________________ =  -(2b-a)=a-2b

     -(4b^2+2ab+a^2-1)