Wednesday

August 27, 2014

August 27, 2014

Posted by **Brock** on Tuesday, July 10, 2012 at 9:58pm.

13. -1, 11, -121, ...; n = 9

A. 235,794,769

B. 429,981,696

C. -429,981,696

D. 196,495,641

E. -196,495,641

F. -235,794,769

I know that n = # of terms (9)

d = -11

a = -1

formula: n/-11(a + last term)

9/-11(-1 +?)

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 10:46pmyes, 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)

= -196495641

**Related Questions**

Maths - Eric thinks of 2 sequences.One is geometric and the other arithmetic....

Maths - An arithmetic and a geometric sequence have the same first terms.(2).......

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...

Advanced Functions - I need help answering these questions 1. State the Common ...

7th Grade Math for Steve.. or Ms. Sue - Determine whether each sequence is ...

Precalculas - The sum of the first 30 terms of one arithmetic sequence is 300 ...