According to ln( 1-x)=-x-x? /2-x？ /3- .....

Get ln( 1-x/3)=-x/3-x? /(2*3? )-x？ /(3*3? )- .....

So f(x)=ln3-x/3-x? /(2*3? )-x？ /(3*3? )- .....

The convergence domain is | x |