Question

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?

I've gotten to this point so far. S6=11-(-11264)^(-4)
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1-(-4)
I'm having trouble with the negative exponent.

Answer 1

this is the formula for geo

Answer 2

formula for the sum of geo****

Answer 3

a=11, R=-4, and n=6

Answer 4

a1(1-(-4)^6)/1-(-4)

11(1-(-4)^6)/(1+4)

Answer 5

So it would be -9009?

Answer 6

yup

Answer 7

-9009; and since the terms are few in number we can double check with brute math if need be

Answer 8

Thanks for the help.

Answer 9

11 + 11(-4) + 11(-4)^2+ 11(-4)^3+ 11(-4)^4+ 11(-4)^5

11( 1 - 4 + 16 - 64 + 256 - 1024)

11( 273 - 1092)

11( -819)

-819
-819
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-9009