HP 50g Graphing Calculator - Manual (Page 176)

Page 4-9
Functions from the MTH menu
The hyperbolic functions and their inverses, as well as the Gamma, PSI, and Psi
functions (special functions) were introduced and applied to real numbers in
Chapter 3. These functions can also be applied to complex numbers by
following the procedures presented in Chapter 3. Some examples are shown
below:
The following screen shows that functions EXPM and LNP1 do not apply to
complex numbers. However, functions GAMMA, PSI, and Psi accept complex
numbers:
Function DROITE: equation of a straight line
Function DROITE takes as argument two complex numbers, say, x
1
+iy
1
and
x
2
+iy
2
, and returns the equation of the straight line, say, y = a+bx, that
contains the points (x
1
,y
1
) and (x
2
,y
2
). For example, the line between points
A(5,-3) and B(6,2) can be found as follows (example in Algebraic mode):
Note: When using trigonometric functions and their inverses with complex
numbers the arguments are no longer angles. Therefore, the angular measure
selected for the calculator has no bearing in the calculation of these functions
with complex arguments. To understand the way that trigonometric functions,
and other functions, are defined for complex numbers consult a book on
complex variables.