*numbers*. Castle are often our development into math and also a salient means that mathematics is discovered in the real world.

You are watching: Any number that can be written as a ratio of two integers

So what *is* a number?

It is not an easy question to answer. It to be not constantly known, for example, just how to write and perform arithmetic v zero or an unfavorable quantities. The notion of number has evolved over millennia and has, at least apocryphally, expense one old mathematician his life.

## Natural, Whole, and Integer Numbers

The most common numbers that us encounter—in everything from speed limits to serial numbers—are **natural numbers**. These room the counting number that start with 1, 2, and also 3, and go ~ above forever. If we start counting indigenous 0 instead, the collection of numbers room instead called **whole numbers**.

While these room standard terms, this is also a chance to share exactly how math is at some point a human endeavor. Different civilization may give different names to these sets, also sometimes reversing i beg your pardon one they call *natural* and also which one they contact *whole*! open it approximately your students: what would certainly they contact the collection of numbers 1, 2, 3...? What new name would certainly they offer it if they consisted of 0?

The **integer**** numbers** (or simply **integers**) extend whole numbers to your opposites too: ...–3, –2, –1, 0, 1, 2, 3.... Notice that 0 is the only number whose opposite is itself.

## Rational Numbers and More

Expanding the ide of number more brings us to **rational numbers**. The name has nothing to carry out with the numbers being sensible, return it opens up a possibility to comment on ELA in mathematics class and show just how one word have the right to have numerous different interpretations in a language and the prestige of being precise with language in mathematics. Rather, words *rational* originates from the root word *ratio*.

A rational number is any type of number that can be composed as the *ratio* of 2 integers, such as \(\frac12\), \(\frac78362,450\) or \(\frac-255\). Note that when ratios can constantly be expressed together fractions, they can show up in various ways, too. Because that example, \(\frac31\) is commonly written as merely \(3\), the portion \(\frac14\) often appears as \(0.25\), and one can write \(-\frac19\) together the repeating decimal \(-0.111\)....

Any number that cannot be created as a reasonable number is, logically enough, referred to as an **irrational**** number**. And also the entire group of all of these numbers, or in various other words, every numbers that have the right to be presented on a number line, are referred to as **real** **numbers**. The power structure of genuine numbers looks something like this:

An essential property that applies to real, rational, and also irrational number is the **density property**. It says that between any type of two actual (or rational or irrational) numbers, over there is always another real (or rational or irrational) number. Because that example, between 0.4588 and also 0.4589 exists the number 0.45887, in addition to infinitely countless others. And also thus, right here are every the feasible real numbers:

## Real Numbers: Rational

*Key standard: recognize a rational number together a proportion of two integers and allude on a number line. (Grade 6)*

**Rational Numbers: **Any number that deserve to be written as a proportion (or fraction) of two integers is a rational number. The is usual for students come ask, space fractions rational numbers? The answer is yes, but fractions comprise a huge category that additionally includes integers, end decimals, repeating decimals, and fractions.

**integer**can be composed as a portion by offering it a denominator of one, so any kind of integer is a rational number.\(6=\frac61\)\(0=\frac01\)\(-4=\frac-41\) or \(\frac4-1\) or \(-\frac41\)A

**terminating decimal**have the right to be composed as a fraction by using properties of location value. For example, 3.75 =

*three and seventy-five hundredths*or \(3\frac75100\), which is same to the improper fraction \(\frac375100\).A

**repeating decimal**can constantly be composed as a portion using algebraic approaches that are beyond the border of this article. However, the is vital to recognize that any kind of decimal v one or an ext digits the repeats forever, for instance \(2.111\)... (which can be created as \(2.\overline1\)) or \(0.890890890\)... (or \(0.\overline890\)), is a reasonable number. A typical question is "are repeating decimals rational numbers?" The answer is yes!

**Integers:** The counting numbers (1, 2, 3,...), their opposites (–1, –2, –3,...), and also 0 room integers. A typical error for students in grades 6–8 is to assume the the integers refer to an adverse numbers. Similarly, plenty of students wonder, space decimals integers? This is only true once the decimal ends in ".000...," as in 3.000..., i beg your pardon is equal to 3. (Technically the is likewise true once a decimal ends in ".999..." due to the fact that 0.999... = 1. This doesn"t come up an especially often, but the number 3 can in reality be written as 2.999....)

**Whole Numbers:** Zero and the positive integers room the entirety numbers.

**Natural Numbers: **Also called the counting numbers, this collection includes all of the totality numbers other than zero (1, 2, 3,...).

## Real Numbers: Irrational

*Key standard: know that there are numbers that there room not rational. (Grade 8)*

**Irrational Numbers: **Any genuine number the cannot be composed in fraction kind is one irrational number. These numbers encompass non-terminating, non-repeating decimals, for example \(\pi\), 0.45445544455544445555..., or \(\sqrt2\). Any kind of square root the is no a perfect root is one irrational number. For example, \(\sqrt1\) and also \(\sqrt4\) are rational since \(\sqrt1=1\) and also \(\sqrt4=2\), yet \(\sqrt2\) and \(\sqrt3\) are irrational. All 4 of this numbers carry out name point out on the number line, however they cannot every be composed as integer ratios.

## Non-Real Numbers

So we"ve gone v all genuine numbers. Space there other types of numbers? for the inquiring student, the price is a resounding correct! High institution students usually learn about facility numbers, or numbers that have actually a *real* part and an *imaginary* part. Castle look favor \(3+2i\) or \(\sqrt3i\) and administer solutions come equations favor \(x^2+3=0\) (whose systems is \(\pm\sqrt3i\)).

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In part sense, facility numbers mark the "end" the numbers, return mathematicians are always imagining new ways to describe and also represent numbers. Number can also be abstracted in a range of ways, consisting of mathematical objects like matrices and sets. Encourage her students to it is in mathematicians! how would they define a number the isn"t among the species of numbers shown here? Why could a scientist or mathematician try to carry out this?

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