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Find the sum of the first 13 terms of the geometric sequence shown below


4, 12, 36, 108, .........


The sum of the first 13 terms is?

Verified Answer :

apologiabiology

the sum of a geometric sequence with  a common ratio or r and a fist term of a1 and summing to term n is
\(\frac{a_1(1-r^n)}{1-r}\)
common ratio is 3=r
first term is 4
13 terms
\(\frac{4(1-3^13)}{1-3}\)=
\(\frac{4(1-3^13)}{-2}\)=
3188644

4,  12 ,36, 108, 324, 972, 2916,8748, 26244, 78732, 236196, 708588, 2,125,764.
All the sums are multiplied by 3.

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