HP 39g+ - Manual (Page 144)

10-8 Using mathematical functions
Complex number functions
These functions are for complex numbers only. You can also
use complex numbers with all trigonometric and hyperbolic
functions, and with some real-number and keyboard
functions. Enter complex numbers in the form (x,y), where x
is the real part and y is the imaginary part.
ARG Argument. Finds the angle defined by a complex number.
Inputs and outputs use the current angle format set in Modes.
ARG ((x,y))
Example
ARG((3,3)) returns 45 (Degrees mode)
CONJ Complex conjugate. Conjugation is the negation (sign
reversal) of the imaginary part of a complex number.
CONJ ((x,y))
Example
CONJ((3,4)) returns (3,-4)
IM Imaginary part, y, of a complex number, (x,y).
IM ((x,y))
Example
IM((3,4)) returns 4
RE Real part x, of a complex number, (x,y).
RE ((x,y))
Example
RE((3,4)) returns 3