Informally, a definable real number is a real number that can be uniquely specified by its description. The description may be expressed as a construction or as a formula of a formal language. For example, the positive square root of 2, , can be defined as the unique positive solution to the equation , and it can be constructed with a compass and straightedge. Different choices of a formal language or its interpretation give rise to different notions of definability. Specific varieties of definable numbers include the constructible numbers of geometry, the algebraic numbers, and the computable numbers. Because formal languages can have only countably many formulas, every notion of definable numbers has at most countably many definable real numbers. However, by Cantor's diagonal argument, there are uncountably many real numbers, so almost every real number is undefinable. (Wikipedia).
What are Real Numbers? | Don't Memorise
Watch this video to understand what Real Numbers are! To access all videos on Real Numbers, please enroll in our full course here - https://infinitylearn.com/microcourses?utm_source=youtube&utm_medium=Soical&utm_campaign=DM&utm_content=3YwrcJxEbZw&utm_term=%7Bkeyword%7D In this video, w
From playlist Real Numbers
Ex: Determine a Real, Imaginary, and Complex Number
This video explains how decide if a number is best described by the set of real, imaginary, or complex numbers. Library: http://mathispower4u.com Search: http://mathispower4u.wordpress.com
From playlist Performing Operations with Complex Numbers
Identifying Sets of Real Numbers
This video provides several examples of identifying the sets a real number belongs to. Complete Video Library: http://www.mathispower4u.com Search by Topic: http://www.mathispower4u.wordpress.com
From playlist Number Sense - Properties of Real Numbers
Tutorial - What is an imaginary number
http://www.freemathvideos.com In this video playlist you will learn everything you need to know with complex and imaginary numbers
From playlist Complex Numbers
Algebraic numbers are countable
Transcendental numbers are uncountable, algebraic numbers are countable. There are two kinds of real numbers: The algebraic numbers (like 1, 3/4, sqrt(2)) and the transcendental numbers (like pi or e). In this video, I show that the algebraic numbers are countable, which means that there
From playlist Real Numbers
Geometry of Complex Numbers (2 of 6: Real vs. Complex)
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From playlist Introduction to Complex Numbers
Imaginary numbers are any numbers that include the imaginary number i. A mix of imaginary and real numbers gives you what’s called a complex number. The primary reason we use imaginary numbers is to give us a way to find the root (radical) of a negative number. There’s no way to use real
From playlist Popular Questions
Ordered Fields In this video, I define the notion of an order (or inequality) and then define the concept of an ordered field, and use this to give a definition of R using axioms. Actual Construction of R (with cuts): https://youtu.be/ZWRnZhYv0G0 COOL Construction of R (with sequences)
From playlist Real Numbers
What is infinity? Can there be different sizes of infinity? Surprisingly, the answer is yes. In fact, there are many different ways to make bigger infinite sets. In this video, a few different sets of infinities will be explored, including their surprising differences and even more surpris
From playlist Summer of Math Exposition 2 videos
Analytic Continuation and the Zeta Function
Where do complex functions come from? In this video we explore the idea of analytic continuation, a powerful technique which allows us to extend functions such as sin(x) from the real numbers into the complex plane. Using analytic continuation we can finally define the zeta function for co
From playlist Analytic Number Theory
What is General Relativity? Special Lecture: Tangent Spaces and Coordinate Basis
What is General Relativity? Special Lecture: Tangent Spaces and Coordinate Basis This is a LONG lecture covering a narrow but important topic: tangent spaces and the coordinate basis. It is intended for anyone who has trouble understanding why a manifold has a vector space at every point
From playlist What is a Manifold?
Construction of the Real Numbers
Dedekind Cuts In this video, I rigorously construct the real numbers from the rational numbers using so-called Dedekind Cuts. It might seem complicated at first, but the advantage is that we can construct the real numbers without using any axioms. More importantly, in the next video, we u
From playlist Real Numbers
11/16/2019, Jonathan Kirby, University of East Anglia
Jonathan Kirby, University of East Anglia Local Definability of Holomorphic Functions Given a collection F of complex or real analytic functions, one can ask what other functions are obtainable from them by finitary algebraic operations. If we just mean polynomial operations we get some
From playlist Fall 2019 Kolchin Seminar in Differential Algebra
The first video in a series which will build up to defining the p-adic numbers. In this episode, we break down our intuitive understanding of the real numbers, and build it back up again using the formality of Cauchy sequences. #some2 #SoME2 My Twitter: https://twitter.com/KristapsBalodi
From playlist Summer of Math Exposition 2 videos
Wolfram Physics Project: Working Session Tuesday, Nov. 2, 2021 [Topos Theory]
This is a Wolfram Physics Project working session about Topos Theory in the Wolfram Model. Originally livestreamed at: https://twitch.tv/stephen_wolfram Stay up-to-date on this project by visiting our website: http://wolfr.am/physics Check out the announcement post: http://wolfr.am/
From playlist Wolfram Physics Project Livestream Archive
Who Gives a Sheaf? Part 2: A non-example
In this video we compare two pre-sheaves, one which is a sheaf, and one which is not.
From playlist Who Gives a Sheaf?
http://www.freemathvideos.com In this video playlist you will learn everything you need to know with complex and imaginary numbers
From playlist Simplify Rational Expressions
Peter Scholze - Liquid vector spaces
Talk at the school and conference “Toposes online” (24-30 June 2021): https://aroundtoposes.com/toposesonline/ (joint with Dustin Clausen) Based on the condensed formalism, we propose new foundations for real functional analysis, replacing complete locally convex vector spaces with a vari
From playlist Toposes online