Perry County is also a part of the larger Harrisburg-York-Lebanon, PA Combined Statistical Area (CSA), which combines the populations of Perry County as well as Adams, Cumberland, Dauphin, Lebanon and York Counties in Pennsylvania.
In mathematics, a function is a relation between a set of inputs and a set of permissible outputs with the property that each input is related to exactly one output. An example is the function that relates each real number x to its square x2.
Not all mathematical functions have periods. Some functions, such as f(x) = x, have no recurring values; every value of x gives a different value of f(x). The most well-known periodic functions are the trigonometric functions sine and cosine, both of which have a period of 2pi. The tangent function, tan(x) = sin(x)/cos(x), is also periodic, with a period of pi.