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July 29, 2015

Homework Help: AP Calculus

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

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?

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