8=2³
а³ +8b³ а³ - 8b³
---------------------- - ----------------------- =
a²-2ab+4b² a²+ 2ab+ 4b²
(a+2b)(a²-2ab+4b²) (a-2b)(a²+ 2ab+4b²)
= ---------------------------- - ----------------------------- = (a+2b)-(a-2b) =
a²-2ab+4b² a²+ 2ab+ 4b²
= a+2b-a+2b =4b , b=0,05 ⇒4b=4*0.05=0,2