Negative And Subtract - Texas Instruments TI-82 Keystroke Manual

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-gray 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-82 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-gray 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. Notice that with the error message you have two choices: Goto (go to the
error) and Quit. Choose Goto by pressing 1 or by pressing ENTER (since choice 1 is already
highlighted). The calculator returns to the Home screen with the cursor blinking on the negative
sign which should have been a subtraction sign. While the cursor is there, type a subtraction sign,
which will replace the incorrect negative sign, and then press ENTER to evaluate the expression.
Now the problem has been fixed.
−
5 7 * 6
− −
17 8 13 * 7
− +
4 1 54
−
2 5 6 3 (
TI-82
−
/( ) 6
+
) 4
7