2. (18 pt) Let f(n) and g(n) be positive functions (for any n they give positive values) and f(n)=O(g(n) ). Prove or disprove each of the following statements: (a) (6 pt) g(n)=(f(n)) (b) (6pt)f(n)g(n)=O(g(n)2) (c) (6pt)2f(n)=O(2g(n))