3b / a+1 × a²-1 / 9b

3b/(a+1)(a+1)(a-1) : 9b
= 3b/(a+1)(a+1)(a-1) x 1/9b
(3b dan 9b dibagi dengan 3)
= 1/(a+1)(a+1)(a-1) x 1/3
= 1/3((a+1)(a+1)(a-1)
= 1/3a³ + 3² - 3a + 3

Semoga membantu