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Mathematics 23 Online
OpenStudy (anonymous):

Help please? What is the sum of the geometric sequence -4, 24, -144, ... if there are 6 terms? -159,963 26,660 26,661 159,963

jimthompson5910 (jim_thompson5910):

notice how you multiply each term by -6 to get the next term

jimthompson5910 (jim_thompson5910):

\[\Large -4{\color{red}{*(-6)}} = 24\] \[\Large 24{\color{red}{*(-6)}} = -144\] etc etc

jimthompson5910 (jim_thompson5910):

what is the term that comes after -144?

OpenStudy (anonymous):

864?

jimthompson5910 (jim_thompson5910):

correct

jimthompson5910 (jim_thompson5910):

and then after that?

OpenStudy (anonymous):

I'm not sure

jimthompson5910 (jim_thompson5910):

you keep the pattern going, multiply the last term (in this case, 864) by -6

OpenStudy (anonymous):

Ohhhhh okay. Yeah. I get it now. Thank you!

jimthompson5910 (jim_thompson5910):

the goal is to generate 6 terms, then add them all up

jimthompson5910 (jim_thompson5910):

the good news is that you have 3 already, so you just need 3 more

OpenStudy (anonymous):

Okay. Thanks a bunch!

jimthompson5910 (jim_thompson5910):

sure thing

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