2 Using your calculator for negative numbers
There are two different mathematical uses for the minus sign (-):
- as the symbol for subtraction, as in
- to indicate a negative number such as
.
Corresponding to these there are two different minus sign keys on the calculator:
, which is used for the operation of subtraction, as in 
, which is used for negative numbers, e.g. 
.
In fact, some calculators permit the key to be used for both purposes, but many other calculators require the equivalent of the key to be used for negative numbers. For this reason we shall use to input negative numbers throughout this guide.
Note that if you attempt to use for subtraction, for example , you will generate a Syntax Error.
Activity 6 Subtraction and negative numbers
Calculate each of the following using your calculator. In each case, give your answer as a decimal not as a fraction.
Answer
Remember to press
to obtain a decimal answer.
You may have been surprised that the correct answer to part (5) is negative. According to the BIDMAS rules, the squaring is performed first, then the negative taken. If we wanted to calculate the square of 
, we write this mathematically as 
and would need to use the brackets when evaluating it on a calculator.