# Using - HP -28S Manual

DEC
(degrees)
and
represent your choices of angle mode. Note that the
DEC
label
shows a small square, indicating that the current angle mode is
Degrees.
(Most illustrations in this manual don't show the annunciators. To lo-
cate the (21r) annunciator, see the illustration on page 27.)
Display the first row of the TRIG menu.
I
TRIG
I
These are one-number functions, acting on the number in level 1. For
real numbers, the angle mode affects how SIN
(sine),
COS
(cosine),
and TAN
(tangent)
interpret their arguments, and how ASIN
(arc sine),
ACOS
(arc cosine),
and ATAN
(arc tangent)
express their results.
You'll use the SIN function in the discussion of
7r
that comes next.
Using
7r
The transcendental number
7r
can't be represented exactly in a finite
decimal form. In general, the calculator's 12-digit approximation
(3.14159265359) yields results accurate to 12 digits, which is suffi-
cient for most applications.
The HP-28S also offers a symbolic constant
IT
that represents
7r
ex-
actly. In radians angle mode, the functions SIN, COS, and TAN
recognize the symbolic constant
IT
and produce an exact result. The
functions SIN and COS also recognize
IT /
2.
74
5: Real-Number Functions  