Name: Garry Who is asking: Student Level: Middle Question: what are the equations for geometric and arithmetic sequences? also, what are the equations for finding the sums of those series? Hi Garry, An arithmetic sequence, also called an arithmetic progression, is a sequence that begins with a fixed number, a , and then each subsequent term is found by adding a constant value, d, called the common difference. General Form: a, a + d, a + 2d, a + 3d + . . . A geometric sequence, also called a geometric progression, also begins with a fixed number, a, and then each subsequent term is found by multiplying by a constant value, r, called the common ratio. General Form: a, ar, ar2, ar3, ar4, ... Whereas the arithmetic sequence has a common difference, d, between the terms, a geometric sequence has a common ratio, r. That is, each subsequent term is found by multiplying the previous term by the common ratio. As for the sum of these progressions it is best to remember how to find the sums rather than to memorize formulas. For example see the note Sequences and series Cheers, Leanne and Penny Go to Math Central