A real number less than zero ("0") is called negative. A negative number is expressed by placing a negative () or "minus" sign before the number. Calculations involving negative numbers are important math assignments in the elementary school. Generally, to obtain a negative number you may subtract a positive number from zero. But many scientific calculators have a special function (a key) that allows you to easily obtain a negative counterpart.
Using the "+/" Key

Enter a number on your calculator; for example, enter "23.5."

Press the key "+/" on your calculator.

Read the calculator display; the minus "" appears before the number, indicating that it is negative. In this example, you should read the number "23.5" on the display.
Using Subtraction

Enter zero "0" on your calculator if you model does not have the "+/" key.

Press the key "" and enter the number, for example "45."

Press the "=" key. The number on the display becomes negative, and you can use it in any further calculation. In this example, the number "45" becomes "45."
References
 "Mathematics for Elementary School Teachers";Tom Bassarear; 2007
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