A real number is any element of the set R,which is the union of the set of rational numbers and the set of irrational numbers. in mathematical expressions,unknown or unspecified real numbers are usually represented by lower case italic letters U through z.The
set R gives rise to other sets such as the set of complex numbers and the set of complex numbers. The idea of a real
number (and what makes it "real") is primarily of interest to
theoreticians. Abstract mathematics has potentially far-reaching applications in
communications and computer science, especially in data encryption and security.