## anonymous 4 years ago 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?

1. amistre64

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

2. anonymous

3. amistre64

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

4. amistre64

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

5. amistre64

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

6. anonymous

ok

7. amistre64

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