Originally Posted by

**MechEng** Hello,

How did we determine that...

$\displaystyle \displaystyle a_{n+1} = a_{n}\ \frac{2n+1}{3n+1} , a_{1}=1$

I'm completely lost. We have $\displaystyle a_{n+1}=1$ and $\displaystyle a_n=0$.

Yet we have $\displaystyle \displaystyle\lim_{n\rightarrow\infty}\frac{a_{n+1 }}{a_n}=\frac{2}{3}$

Wouldn't we have $\displaystyle \displaystyle\lim_{n\rightarrow\infty}\frac{a_{n+1 }}{a_n} = \lim_{n\rightarrow\infty}\frac{1}{0}$ = undefined ?

And what does "DE" mean?

Sorry for all the questions, just trying to fully understand this.