(1/3a − b)^3 = (1/3a − b)(1/3a − b)(1/3a − b)= (1/9a^2 - 2/3ab + b^2)(1/3a - b)= 1/27a^3 - 2/9a^2b + 1/3ab^2 - 1/9a^2b + 2/3ab^2 - b^3= 1/27a^3 - 5/9a^2b + 7/3ab^2 - b^3
(1/3a − b)^3 = (1/3a − b)(1/3a − b)(1/3a − b)
= (1/9a^2 - 2/3ab + b^2)(1/3a - b)
= 1/27a^3 - 2/9a^2b + 1/3ab^2 - 1/9a^2b + 2/3ab^2 - b^3
= 1/27a^3 - 5/9a^2b + 7/3ab^2 - b^3