What is the sum of the geometric sequence 1,-6,36... if there are 6 terms

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asked Jul 6, 2017 133k views

3 votes

What is the sum of the geometric sequence 1,-6,36... if there are 6 terms

Mathematics
high-school

FrancescoDS asked

by FrancescoDS

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1 Answer

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$a_1=1;\ a_2=-6;\ a_3=36;\ ...\\\\r=a_2:a_1\to r=-6:1=-6\\\\S_n=(a_1(1-r^n))/(1-r)\\\\a_1=1;\ r=-6;\ n=6\\\\subtitute\\\\S_6=(1(1-(-6)^6))/(1-(-6))=(1-46656)/(1+6)=(46655)/(7)=6665$

Kennesha answered Jul 12, 2017

by Kennesha

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