DragginMath: Flick Down to Extract Signs ⁻#

The dash – symbol means three things in standard math notation: subtract, negate, and negative. The first two are verbs; the last is an adjective. If you are careful with a pen, or with a good enough computer character set, you can write them differently: a−b, -c, ⁻3. But people rarely take the time to do that. People working with keyboards usually just use the – key that is next to 0 on U.S. keyboards. But DragginMath knows the difference between these three forms and writes them correctly.

So there is a difference between ⁻3 and -3.

The first means negative three, where the word negative is an adjective that tells you about the number’s sign. Positive numbers have a sign also, but people don’t usually write the little ⁺ for ⁺3. Negative and positive are words that apply only to numbers, never to variables.

The second is properly read as negate three, where the word negate is a verb. It means “change the sign of whatever comes after.” If whatever comes after is positive, make it negative. If whatever comes after is negative, make it positive. Negate is a word that applies to either numbers or variables.

Sometimes it is necessary to convert a negative number into a number that will be negated. For example, enter and evaluate 0−3. The result is ⁻3, which appears as one node. This is a negative number. Now flick down on that node. The result is -3. This is a number that will be negated.

If you have -3 in an operator tree, you can drag 3 up onto – to convert it into ⁻3. If you have -⁻3 in an operator tree, you can drag ⁻3 up onto – to convert it into 3. Or you can double-tap the – to evaluate. In this case, it does the same thing.