Is true this statements ??
a) If A is a ring, prove that A-module, A[x] is isomorphic with directs sum of Ai. were Ai=A , for i=1,2,3...
, how A-module.
A module over an underlying ring is said to be free if it has a A-basis. Can you write down a basis for ? Can you see why a free A-module is necessarily a direct sum of copies of A?
Hint: Look at the definition of direct sums and see how it corresponds to the definition of a basis.
As an aside, we usually write instead of