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Real–Number Functions 4–5
Example:
Show that cosine (5/7)
π
radians and cosine 128.57° are equal (to four significant
digits).
Keys: Display: Description:
{

}
Sets Radians mode; RAD
annunciator on.
5
7
)
5/7 in decimal format.
|NzR
.)
Cos (5/7)
π
.
{

}
.)
Switches to Degrees mode (no
annunciator).
128.57
R
.)
Calculates cos 128.57°, which
is the same as cos (5/7)
π
.
Programming Note:
Equations using inverse trigonometric functions to determine an angle
θ
, often look
something like this:
θ
= arctan (y
/
x).
If
x = 0, then y
/
x is undefined, resulting in the error:
# & 
. For a program,
then, it would be more reliable to determine
θ
by a rectangular to polar conversion,
which converts (x,y) to (r,
θ
). See "Coordinate Conversions" later in this chapter.