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General Term of a Geometric Sequence

The general term (nnth term) of a geometric sequence provides a formula for calculating the value of any term directly from its position number, the first term, and the common ratio. For a geometric sequence with first term a1a_1 and common ratio rr, the nnth term is given by:

an=a1rn1a_n = a_1 r^{n-1}

This formula is derived by examining the pattern formed when each successive term is written in terms of a1a_1 and rr. The first term is simply a1a_1 (multiplied by rr zero times). The second term is a1ra_1 \cdot r (multiplied by rr once). The third term is a1r2a_1 \cdot r^2 (multiplied by rr twice), and so on. In each case, the exponent on rr is one less than the position number of the term. For the nnth term, a1a_1 is multiplied by rr exactly n1n - 1 times, which gives an=a1rn1a_n = a_1 r^{n-1}.

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Updated 2026-05-25

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