HP -28S Manual page 285

Q:
The keys from [IJ to [[) don't work. What is wrong?
A: You accidentally selected Menu Lock, so the keys from [IJ to [[)
select menus unless you press • first. To turn off Menu Lock, press
.1
MENUS
I.
Q: I
can't find some variables that
I
used earlier. Where did they go?
A: You may have been using the variables in a different directory. If
you can't remember which directory you were using, you'll need to
check all the directories.
Q:
How can
I
determine how much memory is left?
A: Execute t'lEt1
1
ENTER
1
to return the number of bytes available in
memory.
Q:
Why did the cursor change its appearance?
A:
The cursor indicates the current entry mode. The entry modes are
Immediate (empty cursor), Algebraic (partly filled cursor), or Alpha
(filled cursor). The shape of the cursor indicates Replace mode (box
cursor) or Insert mode (arrow cursor). See "How the Cursor Indicates
Modes" on page 172.
Q: I
keyed in a name (or pressed a USER menu key), but the name didn't
go on the stack. Why not?
A:
You entered an
unquoted
name, which refers to the
contents
of a
variable. To put a name on the stack, press
~
first. (See "Quoted and
Unquoted Names" on page 57.)
Q:
When
I
calculate the cube root of
-27,
why isn't the result
-3?
A: Every number has three cube roots, two of which are complex
numbers. The HP-28S returns one of the three roots, called the princi-
pal value. For positive real arguments the principal value is the real
root; for negative real arguments the principal value is one of the
complex roots. To calculate the real
bth
root of a real number
a,
key in
the following program.
Press
~
RROOT
1
STO
1
to store the program in a variable RROOT
(real
root).
You can then find the real cube root of - 27 by typing 27
1
CHS
1
1
ENTER
1
3
1
ENTER
1
RROOT
1
ENTER
I.
284 A: Assistance, Batteries, and Service