Plus–minus sign facts for kids
Quick facts for kids ± |
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Plus–minus sign
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| See also | Error using : Input "2213" is not a hexadecimal value. |
The plus–minus sign, ±, is a special symbol used in many different ways. It looks like a plus sign (+) stacked on top of a minus sign (-).
Most often, this symbol means there are two possible values or choices. One choice uses the "plus" part, and the other uses the "minus" part.
Here are some common places you might see it:
- In math, it shows that an answer could be either a positive number or a negative number.
- In science, it helps explain how exact a measurement is. It shows the range where the true value might be.
- In medicine, it means "with or without" something.
- In engineering, it shows how much a measurement can be different from the perfect size and still be okay. This is called "tolerance."
- In plants, it describes things as "more or less" a certain way.
- In chemistry, it points to a special mix of chemicals.
- In chess, it tells you if one player has a clear advantage over the other.
- In electronics, it can mean a power supply has both positive and negative voltage.
- In language, it can show if a sound has a certain feature, like if your voice is used to make it.
Contents
History of the Plus-Minus Sign
The idea of using a symbol for "plus or minus" isn't new. A version of this sign, which included the French word ou (meaning "or"), was first used in math by Albert Girard in 1626. The symbol we use today, ±, appeared soon after in 1631. It was used in a math book called Clavis Mathematicae by William Oughtred.
How the Sign is Used
In Mathematics
In math problems, the ± symbol is a shortcut. It means you can use either the plus sign (+) or the minus sign (-) in that spot. This helps show two possible answers or two different equations at once.
For example, if you have the equation x2 = 9, the solution is x = ±3. This means x can be either +3 or -3. Both numbers work when you square them.
A very common place to see this is in the quadratic formula. This formula helps solve certain types of equations:
- Failed to parse (Missing <code>texvc</code> executable. Please see math/README to configure.): x = \frac{-b \pm \sqrt{b^2-4ac}}{2a}
This one formula actually gives you two solutions for x. One solution uses the plus sign, and the other uses the minus sign.
Sometimes, you'll see another similar symbol: the minus–plus sign, ∓. This sign is usually used with the ± sign. When you see them together, like in x ± y ∓ z, it means the ∓ sign always has the opposite meaning of the ± sign.
For example, if the ± is a plus, then the ∓ is a minus. If the ± is a minus, then the ∓ is a plus.
In Science and Statistics
When scientists measure things, there's always a little bit of uncertainty. The ± sign helps show this. For example, if a measurement is 5.7 ± 0.2, it means the actual value is probably around 5.7. But it could be anywhere from 5.5 (5.7 minus 0.2) to 5.9 (5.7 plus 0.2).
This range is called the "tolerance" or "margin of error." It tells you how precise the measurement is. Sometimes, this range means there's a good chance the real value falls within that area.
You might also see a percentage used for the error. For example, 230 ±10% V means the voltage is around 230 volts. But it could be 10% higher or 10% lower. That means it could be anywhere from 207 volts to 253 volts.
In Chess
In chess notation, the symbols ± and ∓ are used to show which player has an advantage.
- ± means the white player has a clear advantage.
- ∓ means the black player has a clear advantage.
Other symbols like + and – can show an even stronger advantage. If you see +–, it means white has a very strong, possibly winning, advantage. If you see –+, black has that strong advantage.
How to Type the Plus-Minus Sign
You can type the ± symbol on different computers:
- On Windows: Hold down the Alt key and type 241 or 0177 on the number pad.
- On Macintosh: Hold down the Option and Shift keys, then press the equals sign (=).
- On Unix-like systems (like Linux): Press the Compose key, then + and -.
Similar Characters
The plus–minus sign looks a bit like some Chinese characters. For example, 土 (meaning "earth" or "soil") and 士 (meaning "scholar" or "knight"). The minus–plus sign ∓ looks a bit like 干 (meaning "dry" or "to do").
See also
In Spanish: ± para niños
