determine the sum of the following geometrec sereis.
-1/32+ 1/16...........+ 256
well I know that I would use the formula:
sn=a (1-r^n)/1-r
a=-1/32
r=
n=
okay this were I get lost can you expalin to me what I nedd to do next? thanks for your help!
Hi,
OK, with CaptBlack's answer I understand your problem:
Your serie is: -1/32, 1/16, -1/8, 1/4, -1/2, 1, -2, 4, -8, 16, -32, 64, -128, 256
To get the result there are two different ways:
1) Put together two summands:
-1/32 + 1/16 = 1/32
-1/8 + ¼ = 1/8
-1/2 + 1 = ½
...
you get a final serie: 1/32, 1/8, 1/2, 2, 8, 32, 128
(for confirmation only: 170.65625 = 5461/32)
2) Split your serie into two series. The first one contains all negative summands, the second one the positive summands. Calculate the sums separately. Add the sums (be aware that one sum is negative!)
(for confirmation only: -170.65625 + 341.3125 = 170.65625)
EB