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Geometric series

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Now Playing:Geometric series– Example 1
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  1. Geometric series formula:sn=t1  (rn−1)r−1{s_n} = \frac{{{t_1}\;\left( {{r^n} - 1} \right)}}{{r - 1}}
    Determine the sum of the first twelve terms of the geometric series: 5 – 10 + 20 – 40 + … .

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    Arithmetic sequences
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    Notes
    A geometric series is the sum of a finite number of terms in a geometric sequence. Just like the arithmetic series, we also have geometric series formulas to help us with that.
    The sum of  n  \, n\, terms of a geometric series:

    Sn=t1(rn−1)r−1=r⋅tn−t1r−1\large S_n = \frac{t_1(r^{n}-1)} {r-1} = \frac{r \cdot t_{n} - t_{1}} {r-1}