Negative And Subtract - Texas Instruments TI-82 Keystroke Manual

calculators: the expression containing addition may be entered just as it appears in print or when
written by hand. To evaluate the expression once you have typed it in, press ENTER. For example,
to evaluate 7 + 15, type this expression just as it appears and press ENTER to display the value
22.
To add expressions involving negative numbers, such as 5 + ( − 8), you may type this
expression just as it appears, using the parenthesis keys, and pressing ENTER to obtain the value
−3. Be sure you use the gray negative key—not the blue subtraction key—when you type in the
− 8. (See 5 Negative and Subtract.) It turns out that you could also type in this expression
without using the parentheses, and it will still work: 5 + − 8 will still produce the value −3.
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5

Negative and Subtract

You may have noticed that the calculator has two keys with a minus sign on them. The gray (–)
key in the bottom row of keys is actually the negative key. The negative key is used only to
write the negative of a number. The following numbers and expressions would be entered using
the gray negative key:
−
The blue key in the right-hand column on the keyboard is the subtraction key. It is grouped
with the other keys used to perform the basic four arithmetic operations (addition, subtraction,
multiplication, and division). The subtraction key is used between two numbers to indicate
that a subtraction is to be done. The following expressions would be entered using the blue
subtraction key:
You can tell which of these keys has been used from the screen display, if you look closely.
The negative sign produced by the negative key is one pixel (dot) shorter and placed one pixel row
higher than the subtraction sign produced by the subtraction key.
Be aware that it is a common mistake among new users of the TI-83 to press the wrong one of
these two keys. Sometimes you will get an error message on the calculator screen when you press
ENTER to evaluate an expression. Other times the calculator will do something different from
what you intend.
For example, suppose you wanted to do the subtraction 8−5 on the calculator. First do it the
correct way with the blue subtraction key and press ENTER to evaluate it. Of course, you should
get 3 as the answer. Now enter it the wrong way by using the gray negative key between the 8 and
the 5 and press ENTER to evaluate it. You get an error message (ERR: SYNTAX, which you can
read more about some other time in the Error Conditions portion in the back of the manual which
came with your calculator). What happened? The calculator does not interpret the negative key as
meaning to subtract. The calculator sees this last expression as two numbers written side by side,
8 and −5, with no indication of which operation you wanted to perform on them. Therefore, the
calculator doesn't know what you want done with these numbers. That's why it gave you an error
message. The calculator is smart enough, however to know where the problem probably lies.
−
5 7 * 6
− −
17 8 13 * 7
− +
4 1 54
−
2 5 6 3 (
TI-83
−
/( ) 6
+
) 4
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