Calculator Skills
Handling Negative Numbers Correctly
Mixing up the subtraction key and the negative-sign key is a frequent, avoidable calculator error in SPM.
Two different keys
Most scientific calculators have a separate key for a negative sign, different from the subtraction key. Using the wrong one, especially inside a power or a bracket, changes the answer.
Squaring a negative needs the number in brackets so the sign is squared too.
A worked keystroke sequence with negatives
- To work out (−7) + 3, press the negative-sign key (−), then 7, then +, then 3, then = . The display reads −4.
- Notice the subtraction key − would not start a number here; the (−) key is what makes 7 negative.
- Now compare −6² and (−6)². Enter (−) 6 x² = and you get −36, because the calculator reads it as −(6²).
- Enter ( (−) 6 ) x² = and you get 36, because the bracket squares the whole negative number.
- Same digits, opposite sign, the bracket decides whether the minus is inside or outside the square.
Two keys that look alike but are not
The subtraction key sits between two numbers and means take away; the negative-sign key attaches to a single number and means this value is below zero. Typing the subtraction key where a negative sign is needed either gives a syntax error or silently changes the meaning.
When you enter a negative value, especially at the start of a bracket or after another operation, reach for the (−) key. Reading your line back and confirming each minus is the right kind is a fast, reliable check.
Source:SPM: Format Pentaksiran mulai 2021, Matematik (1449)
Frequently asked questions
Why does my calculator show an error when I start with a minus?
The subtraction key expects a number before it, so starting a line with it can trigger a syntax error. To enter a negative value at the start, use the negative-sign key marked (−) instead.
The two keys look similar but do different jobs, and mixing them up is one of the most common calculator slips.
Why does −6² give a negative answer?
Because the calculator reads −6² as −(6²), squaring first and then applying the minus, which gives −36. If you mean the square of negative six, you must write (−6)² with brackets, and that gives 36.
Whenever you square a negative quantity, put brackets around it so the sign is included in the square.
Do I need brackets around every negative number?
Not always, but bracket a negative number whenever you square or raise it to a power, multiply or divide by it after another operation, or place it in a formula where the sign could be misread. Brackets never change a correct expression, so when unsure it is safer to include them than to risk the wrong sign.