- Adnan Gill

# Why is – ≠ (–)?

Calculators are great tools for math students (and teachers). I own a TI-Nspire and just holding it gives me immense pleasure, but knowing the cool things I can do with it, increases my joy many folds. While my students in calculus and physics class share some of my joy, and skills, in using the calculator, there is no shortage of students who routinely use their calculators incorrectly, often losing points on assignments.

One of the most common mistake I have observed, is using the – key when the use of (–) is warranted. Many calculators, usually Casio models have a +/– key that has the same function as the (–) key in the TI-84 and other TI models.

The two keys have different functions. (–) is the "negative" or "opposite" key. Its purpose is to change the sign of a quantity. Pushing this key before a number changes its sign. This is most commonly done to change a positive number to a negative. The – key, however is the "minus" key and its purpose is to execute a subtraction operation.

Following are some examples of when you should use the (–) key:

Evaluating sin (–π /2)

Evaluating –3/2

Evaluating 3 x –5

Following are some examples of when you should use the – key:

Evaluating 52 – 37

Evaluating 25 – 78

It is important that you use your calculator correctly and effectively. Using the – or (–) appropriately will help you do that.