# Thread: Am I summing this correctly?

1. ## Am I summing this correctly?

I have this series

(1-v^39) + (1-v^36) +(1-v^33).....+(1-v^3)

I added up all the 1's and was left with:

13-(v^3 +v^6....+v^39)

Factored out v^3

13- v^3(1+v^3 +..... v^36)

So I get 13 - v^3 * [(1-v^37)/(1-v)]

2. Originally Posted by babbagandu
I have this series

(1-v^39) + (1-v^36) +(1-v^33).....+(1-v^3)

I added up all the 1's and was left with:

13-(v^3 +v^6....+v^39)

Factored out v^3

13- v^3(1+v^3 +..... v^36)

So I get 13 - v^3 * [(1-v^37)/(1-v)]
I think in the last term you want

$
\frac{1-v^{39}}{1-v^3}
$

3. Originally Posted by Danny
I think in the last term you want

$
\frac{1-v^{39}}{1-v^3}
$

Ooooh. Ok thanks