(a^3+8b^3)/(a+2b)

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

(a+2b)/(a+2b) = 1

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