HP -32S Owner's Manual page 60

Example. Show that the cosine of (5/7)ir radians and the cosine of
128.57° are the same.*
Keys:
Bl MODES | {RD}
5fjNTCR]7[±]IQ0
fcosl
fllMODESl {DG}
128.57 rCQSl
Display:
-8.6235
-0.6235
Description:
Sets Radians mode;
RAD annunciator on.
Cos (5/7)ir.
Switches to Degrees
mode (no annunciator)
and calculates cos
128.57°, which is the
same as cos (5/7)ir.
Programming Note. Equations using inverse trigonometric functions
to determine an angle, 6, often look something like this:
6 = arctan (y/x).
If x = 0, then y -s- x is undefined, resulting in the error
DIVIDE BY 0. For a program, then, it would be more reliable to
determine 6 by a rectangular to polar conversion, which converts x, y to
r, 6. See 'Coordinate Conversions,* later in this chapter.
' Actually, thesecalculated results arethe sameonly to four significant digits due to the inex
act representation of a-. (Press jl]| SHOW Ito see more digits.)
58 4: Real-Number Functions