PLEASE answer quicky! Will give medal: What is the sum of a 6-term geometric sequence if the first term is 11, the last term is –11,264 and the common ratio is –4?

Question

amistre64 · Answer

$$S_n=a\frac{1-r^n}{1-r}$$
here n=6, a=11 and r = -4

anonymous · Answer

the answer is -9,009?

amistre64 · Answer

the numbers you give dont seem to coincide unless that -11,264 is spose to be some random number off in the distance past the 6th term

amistre64 · Answer

well, now they do, i was inputing it wrong in the wolf

amistre64 · Answer

so yeah; that should be it.  you have alternating positives and negatives

anonymous · Answer

ok

amistre64 · Answer

http://www.wolframalpha.com/input/?i=sum+%2811*%28-4%29%5E%28n-1%29%29+from+1+to+6 works out both ways :)