# Arithmetic Series help

#### CathyLou

Please could someone tell me the way to find the smallest positive term of an arithmetic series (C1 level) as I cannot find a formula anywhere.

Thank you.

Cathy

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#### cristo

Staff Emeritus
You could rearrange the formula $$S_n=\frac{n[2a_1+(n-1)d]}{2}$$, where n is the numbers of terms, Sn is the sum of the first n terms, d is the difference between the ith and (i+1)th term, and a1 is the first term of the series.

#### CathyLou

You could rearrange the formula $$S_n=\frac{n[2a_1+(n-1)d]}{2}$$, where n is the numbers of terms, Sn is the sum of the first n terms, d is the difference between the ith and (i+1)th term, and a1 is the first term of the series.