# How do you write all real numbers in set notation

Starting Out Ready, set, go! Alright, let's get started! We first prove the following result about fractions: Then a2 and b2 also have no common factors, because if any prime p were a common factor of a2 and b2, it would also be a common factor of a and b. Hence is not a whole number. Since is not a whole number, but its square is the whole number 2, it follows from the above result that is not a rational. This caused great upset to the Greek mathematicians, since it introduced a new sort of number which they called an irrational number.

An older word for this is incommensurable, which meant that it could not be measured as a ratio of two whole numbers. This discovery caused a dramatic rethink into the nature of number. The validity of many of their geometric proofs, which assumed that all lengths could be measured as ratios of whole numbers, was also called into question.

The proof given above can easily be adapted to prove that if a whole number x is not an nth power, then is not a rational number.

Thus we have infinitely many examples of irrational numbers, such as: Solution As with the proof that is irrational, we begin by supposing the contrary. Thus, log2 5 is irrational. The real numbers Think about graphing the rational numbers between 0 and 2 on the number line.

## Set-Builder Notation

First we graph1then the thirds, then the quarters, then the fifths, …. As we keep going, the gaps between the dots get smaller and smaller, and as we graph more and more rational numbers, the largest gap between successive dots tends to zero.

If we imagine the situation when all the infinitely many rational numbers have been graphed, there appears to be no gaps at all, and the rational numbers are spread out like pieces of dust along the number line.

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Surely every point on the number line has been accounted for by some rational number? There are infinitely many numbers that we have not graphed, all rational multiples ofincluding: Of course, there are many more missing numbers, like and log2 3 and.

The solution is very simple — we make an appeal to geometry and define numbers using the geometrical idea of points on a line: Definition The real numbers are all of the points on the number line.

The set of real numbers consists of both the rational numbers and the irrational numbers. Constructing real numbers We have seen in the module Constructions that every rational number can be plotted on the number line.

For example, to plot we first divide the interval from 0 to 1 into 5 equal subinterval this requires the construction of Thus rational numbers are indeed special cases of real numbers.

For example, to plot we first construct a square on the interval from 0 to 1 the constructions of the right angles are not shown on the diagram. Then we draw the diagonal from 0, which has lengthand use compasses to place this length on the number line. The real numbers and the rational numbers We have seen that as we place halves, thirds, quarters, fifths, … on the number line, the maximum gap between successive fractions tends to zero.

Thus we can use rational numbers to approximate a real number correct to any required order of accuracy. These observations might lead one to believe naively that the rational and irrational numbers somehow alternate on the number line.

## Mathematical Notation: Past and Future

Nothing could be further from the truth. Even though there are infinitely many rational numbers and infinitely many irrational numbers between 0 and 1, there are vastly more real numbers in that interval than rational numbers.

This spectacular, but rather vague, claim can be made into a theorem as precise as any other mathematics, and proven rigorously — see the Appendix 2 for the details, which are an excellent challenge for interested and able students. Intuitively, one should see the real number line as a continuum, with the points joined up to make a line, whereas the rational numbers are like disconnected specks of dust scattered along it.

The real numbers and decimals We have seen that every rational number can be written as a terminating or recurring decimal.

Conversely, every terminating or recurring decimal can be written as a fraction, and thus as a rational number. Now suppose that we have a decimal that is neither terminating nor recurring, such as 1.

This decimal represents a definite point on the number line, and so is a real number, but it is not a rational number, because it neither terminates nor recurs. Indeed, any infinite decimal that is neither terminating nor recurring represents an irrational real number, and two different such infinite decimals represent different real numbers.

As we add tenths, hundredths, thousandths. The conclusion of all this is the following theorem. If the expansion terminates or recurs, the number is rational, otherwise the number is irrational. The two simplest are described below. This method of approximating real numbers by terminating decimals of whatever length is required is one reason why decimal expansions are so useful in science and everywhere that mathematics is applied.

Arithmetic with real numbers — using approximations Having defined real numbers as points on the number line, how are we to define addition, subtraction, multiplication and division of real numbers?

The most obvious approach is to work with their decimal expansions, and add, subtract, multiply and divide suitable truncations of these expansions.In mathematics (real), the interval is a set of real numbers with the property that any number between two numbers in the set is also included in the set.

For example, the set of all numbers x satisfying 0 ≤ x ≤ 1 is an interval that contains 0 . Hi all, the informations and hints I have read here are all really helpful. I think it is best to avoid the use of seq.

The reason is that some scripts need to be portable and must run on a wide variety of unix systems, where some commands may not be present.

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In mathematics, a real number is a value of a continuous quantity that can represent a distance along a schwenkreis.com adjective real in this context was introduced in the 17th century by René Descartes, who distinguished between real and imaginary roots of schwenkreis.com real numbers include all the rational numbers, such as the integer −5 and the fraction 4/3, and all the irrational numbers.

The real numbers. Think about graphing the rational numbers between 0 and 2 on the number line. First we graph, 1, then the thirds, then the quarters, then the fifths, .As we keep going, the gaps between the dots get smaller and smaller, and as we graph more and more rational numbers, the largest gap between successive dots tends to zero.

You never know when set notation is going to pop up. Usually, you'll see it when you learn about solving inequalities, because for some reason saying " x you to phrase the answer as "the solution set is { x | x is a real number and x.

BioMath: Mathematical Notation