(a+b)³-(a-b)³=a³+3a²b+3ab²+b³-(a³-3a²b+3ab²-b³)=
=a³+3a²b+3ab²+b³-a³+3a²b-3ab²+b³=6a²b-6ab².
Тогда
(((a+b)³-(a-b)³)/2b(3a²+b²)) +1 = ((6a²b-6ab²)+2b(3a²+b²))/2b(3a²+b²)=
= (6a²b-6ab²+6a²b+2b³)/(2b(3a²+2b²))=(12a²b-6ab²+2b³)/(2b(3a²+b²))=
=2b(6a²-3ab+b²)/2b(3a²+2b²)= (6a²-3ab+b²)/(3a²+2b²).