Write an expression for Sn

[teraslintu]

a) Write an expression for Sn, for the series 1 + 7 + 13 + ...

b) Hence, find the value of n for which Sn=833

Please help me.... I don't even know where to begin

 

[Otis]

… I don't even know where to begin

Hello teraslintu. Is this homework?

If you need lessons, you can google "find the arithmetic sequence".

\(\;\)

 

[pka]

a) Write an expression for Sn, for the series 1 + 7 + 13 + ...

Each term is the series is \(\displaystyle a_n=1+6\cdot(n-1)=6n-5\)
\(\displaystyle {S_n} = \sum\limits_{k = 1}^n {(6k - 5)}=~? \)

 

[MarkFL]

Each term is the series is \(\displaystyle a_n=1+6\cdot(n-1)=6n-5\)
\(\displaystyle {S_n} = \sum\limits_{k = 1}^n {(6k - 5)}=~? \)

I've deleted my post since this one makes it obsolete.