a function that describes a set of points in Cartesian space by mapping each x-coordinate to a y-coordinate, then a circle cannot be described by a function because it fails what is known in High School as the vertical line test. A function, by definition, has a unique output for every input.
Well, since we know is a geometric sequence, we can always get the common ratio of it by simply dividing one value by the one behind it... so let's do so, with say hmm -32 and 8 -32/8 = -4 <-- our common ratio