wow !

How can people ( is that you ?) find out this this expression/series for irrational numbers ?

we have

we can see that the series converges so quickly !

for this problem ,

I use a quite complicated method , is there any method better than mine ?

Go through it !

the general term of the seqence is

where

so the product of first

terms is

the series can be written in this form :

To evluate this series , we just need to create

next to the series .

I got

for

I got

or an elegant-appearance

the fifth term is about

, wow