You are watching: Is -1/2 a rational number
So what is a number?
It is not a simple question to answer. It was not always known, for example, how to write and perform arithmetic through zero or negative quantities. The concept of number has advanced over centuries and has, at leastern apocryphally, expense one ancient mathematician his life.
Natural, Whole, and also Integer Numbers
The the majority of common numbers that we encounter—in everything from speed boundaries to serial numbers—are herbal numbers. These are the counting numbers that begin through 1, 2, and also 3, and also go on forever. If we start counting from 0 instead, the collection of numbers are instead called whole numbers.
While these are traditional terms, this is also a chance to share exactly how math is inevitably a human endeavor. Different civilization might offer different names to these sets, also occasionally reversing which one they contact natural and which one they contact whole! Open it approximately your students: what would they contact the set of numbers 1, 2, 3...? What brand-new name would they give it if they had 0?
The integer numbers (or simply integers) extfinish entirety numbers to their opposites too: ...–3, –2, –1, 0, 1, 2, 3.... Notice that 0 is the just number whose oppowebsite is itself.
Rational Numbers and More
Expanding the idea of number better brings us to rational numbers. The name has actually nopoint to perform via the numbers being wise, although it opens up a chance to talk about ELA in math course and show exactly how one word deserve to have many type of different interpretations in a language and the prominence of being precise through language in math. Rather, the word rational comes from the root word ratio.
A rational number is any number that have the right to be written as the ratio of two integers, such as (frac12), (frac78362,450) or (frac-255). Keep in mind that while ratios deserve to always be expressed as fractions, they can appear in different methods, also. For instance, (frac31) is usually written as simply (3), the fraction (frac14) often shows up as (0.25), and also one can write (-frac19) as the repeating decimal (-0.111)....
Any number that cannot be created as a rational number is, logically enough, referred to as an irrational number. And the whole category of all of these numbers, or in other words, all numbers that deserve to be presented on a number line, are called real numbers. The power structure of real numbers looks somepoint choose this:
An necessary home that uses to actual, rational, and also irrational numbers is the density property. It claims that in between any two real (or rational or irrational) numbers, tright here is always one more actual (or rational or irrational) number. For example, between 0.4588 and 0.4589 exists the number 0.45887, in addition to infinitely many kind of others. And therefore, right here are all the possible real numbers:
Real Numbers: Rational
Key standard: Understand a rational number as a proportion of two integers and point on a number line. (Grade 6)
Rational Numbers: Any number that have the right to be written as a proportion (or fraction) of 2 integers is a rational number. It is common for students to ask, are fractions rational numbers? The answer is yes, yet fractions consist of a big category that also contains integers, terminating decimals, repeating decimals, and fractions.An integer have the right to be written as a portion by giving it a denominator of one, so any type of integer is a rational number.(6=frac61)(0=frac01)(-4=frac-41) or (frac4-1) or (-frac41)A terminating decimal deserve to be composed as a portion by using properties of area value. For example, 3.75 = 3 and also seventy-5 hundredths or (3frac75100), which is equal to the improper fraction (frac375100).A repeating decimal deserve to always be written as a fraction utilizing algebraic approaches that are beyond the scope of this short article. However before, it is crucial to identify that any type of decimal via one or even more digits that repeats forever, for example (2.111)... (which have the right to be composed as (2.overline1)) or (0.890890890)... (or (0.overline890)), is a rational number. A prevalent question is "are repeating decimals rational numbers?" The answer is yes!
Integers: The counting numbers (1, 2, 3,...), their opposites (–1, –2, –3,...), and 0 are integers. A prevalent error for students in Grades 6–8 is to assume that the integers describe negative numbers. Similarly, many kind of students wonder, are decimals integers? This is only true when the decimal ends in ".000...," as in 3.000..., which is equal to 3. (Technically it is likewise true once a decimal ends in ".999..." because 0.999... = 1. This doesn"t come up especially often, but the number 3 can in truth be written as 2.999....)
Whole Numbers: Zero and also the positive integers are the entirety numbers.
Natural Numbers: Also called the counting numbers, this collection has every one of the entirety numbers except zero (1, 2, 3,...).
Real Numbers: Irrational
Key standard: Kcurrently that there are numbers that tright here are not rational. (Grade 8)
Irrational Numbers: Any actual number that cannot be written in fractivity create is an irrational number. These numbers encompass non-terminating, non-repeating decimals, for example (pi), 0.45445544455544445555..., or (sqrt2). Any square root that is not a perfect root is an irrational number. For example, (sqrt1) and (sqrt4) are rational bereason (sqrt1=1) and also (sqrt4=2), yet (sqrt2) and (sqrt3) are irrational. All 4 of these numbers perform name points on the number line, but they cannot all be written as integer ratios.
So we"ve gone with all real numbers. Are tright here other types of numbers? For the inquiring student, the answer is a resounding YES! High college students primarily learn about complex numbers, or numbers that have actually a real part and an imaginary part. They look favor (3+2i) or (sqrt3i) and provide solutions to equations choose (x^2+3=0) (whose solution is (pmsqrt3i)).
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In some feeling, complex numbers mark the "end" of numbers, although mathematicians are always imagining new methods to explain and reexisting numbers. Numbers can also be abstracted in a selection of methods, including mathematical objects like matrices and sets. Encourage your students to be mathematicians! How would certainly they describe a number that isn"t among the kinds of numbers presented here? Why might a scientist or mathematician try to do this?
Looking for a math curriculum that will thrive student confidence in mathematics and also help learners exploit rational and also irrational numbers? Explore HMH Into Math, our core math solution for Grades K–8.