math

Find the sum of the first 15 terms of the geometric sequence.


Σ 3n − 1
n = 1

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  1. this is just an arithmetic sequence with
    a=2
    d=3
    So, S15 = 15/2 (2*2+14*3)

    If you really wanted a geometric sequence, the I assume you meant

    Σ3^(n-1)

    In that case,
    a=1
    r=3
    so S15 = 1*(3^15-1)/(3-1)

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