Which of the following is a characteristic of complex numbers?

A characteristic of complex numbers is that they have real and imaginary parts. A complex number is typically expressed in the form ( a + bi ), where ( a ) represents the real part and ( b ) represents the coefficient of the imaginary part, which is denoted by ( i ), the imaginary unit defined as the square root of -1. This structure allows complex numbers to encompass a broad range of values beyond just real numbers, providing a way to represent solutions to equations that have no real solutions, such as ( x^2 + 1 = 0 ).

The other options do not accurately describe complex numbers. For instance, complex numbers are not restricted to positive values, nor are they limited to being expressed as integers; they can also include fractions and irrational numbers within both their real and imaginary components. Hence, the defining characteristic concerning the division into real and imaginary parts highlights the unique nature of complex numbers within mathematics.