A GEOMETRIC Series
Whenever a series of numbers follow a pattern of multiplying a term by a constant each term to arrive at the next term, we regard such a sequence as a geometric sequence. The constant multiplied each time is the same. This fixed constant that is being multiplied to arrive at the next term is called the common ratio, r, referring to the fact that the ratio (fraction) of the second term to the first term yields this constant. To find the common ratio, divide the second term by the first term or any two sequences that alternate, always dividing first by the second.