Quick question (1 Viewer)

[Yoko Hono]

Hi,

Just wondering whether anyone could tell which formula for the sum of a geometric series to use when r is a fraction between -1 and 1.

Is it Sn = a(r^n - 1) over r-1

OR is it

Sn = a(1-r^n) over 1-r

?

Thanks

 

[Captain Gh3y]

1 - r for a positive fraction would be easier... it doesn't make any difference apart from making the calculations have more or less negative signs.

 

[Yoko Hono]

Thanks heaps for that and good luck tomorrow.

 

[sunjet]

r - 1 when r > 1
1 - r when r < 1