Hello,

the problem is to calculate inverse element (reciprocal) of in ring .

I skimmed some Wikipedia and found following formula:

Inverting series

But I don't know to use it. Also the following model answer didn't help me either:

"Task is to calculate inverse element (reciprocal) of in the ring .

So, we have to calculate that

.

When the is solved, and then ..., we see that inverse element is "

I don't understand how those etc. are solved. Only thing, that is clear to me is, that is generated by , which equals .

So, any help is appreciated. Thanks very much!