Step-by-step explanation: Basically an asymptote is a line that approaches a given curve which is graph of a function, but it never touches, cross or intersect in any finite. Asymptote can be any line, horizontal, vertical, inclined, which approaches the function graph. Theoretically, according to mathematical principles, the function graph line is approaching to a asymptote at infinity, and therefore the asymptotes are suitable as the type of guide to complete the graph of the function.
In Maths, an asymptote is a line that the graph (a drawing that shows two sets of related amounts) of a function (e.g. x=1/x) approaches but does not cross (or intersect). The image below illustrates such concept.
r^2 (r represents your radius of 4 feet)