Ответ:

4b³+8b/b³-8 - 2b²/b²+2b+4 = 4b³+8b/(b-2)(b²+2b+4) - 2b²/b²+2b+4 = 4b³+8b-2b²(b-2)/(b-2)(b²+2b+4) = 4b³+8b-2b³+4b²/(b-2)(b²+2b+4) = 2b(b²+4+2b)/(b-2)(b²+2b+4) = 2b/b-2