1) (1/2a-1/3b)^3 2) (0,5a+0,1b)^3 (a-b)^3-a^2+2ab-b^2

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

1)(1/2a-1/3b)^3=0,125a^3-0,25a^2b+1/12ab^2-1/27

2)(0,5a+0,1b)^3=0,125a^3+0,075a^2b+0,015ab^2+0,001b^3

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