Complex numbers have two parts: the “real” part (any real number) and an “imaginary” part (any number with an *i* in it). The standard complex number format is “*a* + *bi*,” or a real number plus an imaginary number. It is also often seen as *x* + *iy*, because while real numbers are viewed on a line, complex numbers are viewed graphically on an Argand (or polar) coordinate system: The imaginary numbers make up the vertical (or *y*) axis as *iy*, while the horizontal (or *x*) axis is occupied by real numbers. (For more information about coordinate systems, see “Geometry and Trigonometry.”)