Posted by **Anonymous** on Sunday, September 18, 2011 at 8:00pm.

How many terms are required in the series (-6) + (-12) + (-24)... to add to a sum of -378?

How do I do this?

- Calculus -
**Reiny**, Sunday, September 18, 2011 at 8:04pm
looks like a geometric series where

a = -6 and r = 2

Term(n) = a(r^n - 1)/(r-1), where n is the number of terms

-378 = -6(2^n - 1)/(2-1)

63 = 2^n - 1

64 = 2^n

I know that 2^6 = 64

so n=6

so you need 6 terms.

- Calculus -
**Anonymous**, Sunday, September 18, 2011 at 8:10pm
Thank you so much, could you please help me with my other calculus posts.

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