Which of the following best describes the expression below when

A. Rational number
B. Irrational number
C. Real number
D. Complex number

The expression is best described as a complex number. Complex numbers are of the form , where and are real numbers, and represents the imaginary unit, which is the square root of -1. So, is the real part and is the imaginary part.

In mathematics, complex numbers are incredibly useful, especially in fields like engineering, physics, and applied mathematics. They allow for the solution of equations that do not have real solutions and are indispensable in analyzing waveforms, oscillations, and other phenomena that can be modeled using sinusoidal functions.