Posted by Brock on Tuesday, July 10, 2012 at 9:58pm.
Find the sum of the first n terms of the sequence. The sequences are either arithmetic or geometric.
13. -1, 11, -121, ...; n = 9
I know that n = # of terms (9)
d = -11
a = -1
formula: n/-11(a + last term)
Also term 4 = 1331
But, the last term is too large (-214358881).
Am I doing something wrong?
AP Calculus - Brock, Tuesday, July 10, 2012 at 10:10pm
* The sequence is geometric and the r=-11. Thank you for any help!
AP Calculus - Reiny, Tuesday, July 10, 2012 at 10:46pm
yes, you realized that the series was geometric rather than arithmetic
so you have
a=-1, r = -11, n = 9
you now need the formula for the sum of a geometric, not arithmetic like you stated.
sum(n) = a(r^n - 1)/(r-1)
= -1( (-11)^9 - 1)/(-11-1)
Answer This Question
More Related Questions
- Maths - Eric thinks of 2 sequences.One is geometric and the other arithmetic....
- math - in an arithmetic sequence the common difference is equal to 2.the first ...
- Maths - An arithmetic and a geometric sequence have the same first terms.(2).......
- Math Help!!! - determine whether each sequence is arithmetic or geometric. find ...
- Maths - 1..The first 2 terms of a geometric progression are the same as the ...
- Math *URGENT - Please give the answers and solutions for each. 1.If the second ...
- Algebra - Determine whether each sequence is arithmetic or geometric. Find the ...
- Can someone help me?! - The 1st, 5th and 13th terms of an arithmetic sequence ...
- math - Determine whether each sequence is arithmetic or geometric. Find the next...
- Maths - The first, third and ninth terms of an arithmetic sequence form the ...