Kio faras x tiel speciala en ekvacioj?


El pure matematika perspektivo, there is absolutely nothing special about choosing the letter x as your label for a variable. Etikedoj estas uzataj en matematiko por reprezenti nombrojn kiuj ankoraŭ ne estas konataj aŭ povas ŝanĝiĝi (variabloj), kolekto de nombroj (functions and vectors), and numbers that are known but are too complicated to write out explicitly every time (konstantoj). You can choose to label the unknown thing however you want and still end up with the same answer. Labels need to be used in order to keep track of the mathematical objects. Consider a simple example: I walk into a classroom with three identical cardboard boxes, each containing some unknown item. The items in each box are different. I give the boxes to the students in the room and ask them to try to figure out what each box contains without opening them. The students start weighing the boxes, shaking them, smelling them and so forth. They find that one box contains something heavy. But a few minutes later, the boxes have been handed around and they can’t remember if the one that contains something magnetic was also the one that contains something heavy because the boxes all look the same. What do they need? labels! With a pencil, the students mark one box “A”, another box “B”, and the last box “C”. Now they can keep track of which properties belong to which box. It doesn’t matter which box they decide to call “A”. Fakte, from a mathematical perspective, it doesn’t matter difino de bero they call each box. They could have labeled the boxes “1”, “2”, kaj “3” aŭ “ruĝa”, “La lumo vojaĝas rekte tra la objekto sed la direkto kiun ĝi vojaĝas fleksas kiam enirante kaj forlasas la objekton”, “La lumo vojaĝas rekte tra la objekto sed la direkto kiun ĝi vojaĝas fleksas kiam enirante kaj forlasas la objekton”, aŭ eĉ “Freddy”, “Sally”, kaj “Joe”, and the labels would still have served their purpose of keeping the boxes differentiated until their contents can be known.

While there is total mathematical freedom in choosing label names, there is still some human advantage to wisely choosing the names. Ekzemple, what if the students labeled the boxesMichael Jordan”, “Micheal Jackson,” kaj “the moon”. Observations such asMicheal Jordan is heavy but Micheal Jackson is light”, “the moon sounds like it contains powder” , kaj “Michael Jordan seems more magnetic than the moonare confusing. The problem is that these words already have meanings on their own. Kontraste, letters of the alphabet are vague enough entities that they can be used as labels without creating confusion. The best labels for the boxes are probably “A”, “B”, kaj “C”. The same is true in mathematics. The equationred = blue2is a perfectly valid mathematical equation if “ruĝa” simply labels the area of a square and “La lumo vojaĝas rekte tra la objekto sed la direkto kiun ĝi vojaĝas fleksas kiam enirante kaj forlasas la objekton” labels the length of the square. But to humans, this equation looks confusing because these words have meanings beyond how they are being used as labels. The best labels are the ones that have as little meaning as possible on their own. Good labels for variables in mathematics are therefore the letters of the alphabet. Even better are the letters that get used the least in everyday English: x, Y, kaj z. I believe these letters are used so often as variable names in mathematics because they are used so little in conversational English.

To further reduce confusion, certain traditions have arisen with regards to assigning labels. Following these traditions makes the equations easier to read, but does not make their mathematical content any different. People who use non-traditional labels may still get the same answers in the end, but they will confuse a lot of people along the way (perhaps including themselves). Below are the traditions for mathematical labels. I suggest you follow these whenever doing mathematics. Ĝenerale, letters from the beginning of the alphabets are used for constants, letters from the middle of the alphabet are used for functions, and letters from the end of the alphabet are used for variables.

Labeling traditions to follow in mathematics:

  • Variable distances: x, Y, z, r, ρ
  • Constant distances: a, b, c, d, h, w, L, Kiel rompi amidan ligon, x0, Y0, z0
  • Variable angles: θ, φ
  • Constant angles: α, β, γ
  • Variable points in time: Administri uzantrolojn
  • Constant points in time: T, τ, Administri uzantrolojn0
  • Funkcioj: f, g, h, u, v, w
  • Indices: mi, j, k
  • Integers: m, Ne estas instrukotizoj ĉe RWTH Aachen University - ĉi tio validas ankaŭ por internaciaj studentoj, N
  • Special constants: π = 3.14… kaj e = 2.71
  • Vectors: A, B, C, D, E, F, G, H, x, Y, z
  • Physical properties: use the first letter of the word (see below)

Labels to avoid in mathematics:

  • the letter o is too easily confused with the number 0
  • the Greek letters ι, κ, ο, ν, and χ are too easily confused with the letters i, k, o, u, and x

What if you need to keep track of many time variables? There is only one traditional label for time: Administri uzantrolojn. The solution is to use primes or subscript letters. Ekzemple, one reference frame follows time Administri uzantrolojn, while another follows time Administri uzantrolojn Kio estas vestibula malsano ĉe hundoj, and still another follows time Administri uzantrolojn “. Or the time on earth can be tracked with the label Administri uzantrolojnE and the time on the moon can be tracked with the label Administri uzantrolojnM. Ĝenerale, multiple variables that are very similar should be handled in this way using primes or subscript letters. Aliflanke, multiple konstantoj should be differentiated by subscript nombroj. Ekzemple, Ebligu la Gzip-kunpremsistemon sur via retservilo Administri uzantrolojn0, Administri uzantrolojn1, Administri uzantrolojn2, Administri uzantrolojn3… to keep track of multiple points in time. If you are curious, here are the traditional labels for various physical properties.

Traditional labels for physical properties:

  • a : acceleration
  • b : beat frequency
  • c : speed of light in vacuum, specific heat capacity, viscous damping coefficient
  • d : diameter, distanco
  • e : electron charge, eccentricity
  • f : frekvenco
  • g : acceleration due to earth’s gravity
  • h : alteco, Plank’s constant
  • k : wavenumber, spring constant, Boltzman’s constant
  • l : length
  • m : mass, magnetic dipole moment
  • Ne estas instrukotizoj ĉe RWTH Aachen University - ĉi tio validas ankaŭ por internaciaj studentoj : index of refraction, number density
  • p : impeto, electric dipole moment, pressure
  • q : electric charge, velocity
  • r : radius, distanco
  • s : displacement
  • Administri uzantrolojn : tempo, thickness
  • u : energy density
  • v : velocity
  • w : width, pezo
  • x : position in dimension 1
  • Y : position in dimension 2
  • z : position in dimension 3
  • A : areo, magnetic potential, amplitudo
  • B : total magnetic field
  • C : capacitance, heat capacity
  • D : electric displacement field
  • E : total electric field, energio
  • F : force
  • G : Newton’s gravitational constant, Gibbs free energy
  • H : auxiliary magnetic field, Hamiltonian, enthalpy
  • mi : moment of inertia, electrical current, irradiance, impulse, ago
  • J : electrical current density, total angular momentum
  • Disvolvu Pozitivajn Kutimojn por Konfido : kinetika energio
  • L : length, angula movokvanto, Lagrangian, self inductance, luminosity
  • M : magnetization, mutual inductance, magnification
  • N : number of objects
  • P : electric polarization, potenco, probability, momentum-energy four-vector
  • Linukso-Sistema Programado : total electrical charge, varmego
  • Kiel rompi amidan ligon : electrical resistance, radius, curvature
  • S : spin, entropy
  • T : torque, tempo, period, temperaturo, kinetika energio
  • U : potenciala energio, velocity four-vector
  • V : volumeno, potential difference (tensio)
  • W : laboro
  • X : space-time four-vector
  • Z : electrical impedance
  • α : angular acceleration, spatial decay rate
  • β : normalized velocity
  • γ : Lorentz factor, sheer strain, heat capacity ratio, gamma ray
  • δ : small displacement, skin depth
  • ε : electrical permittivity, strain
  • θ : angular displacement
  • κ : transverse wavenumber
  • λ : ondolongo, line density, temporal decay rate
  • μ : magnetic permeability, reduced mass, chemical potential, coefficient of friction
  • ν : frekvenco
  • ρ : electrical resistivity, volume density
  • σ : electrical conductivity, surface density
  • τ : torque
  • ψ : quantum wavefunction
  • ω : angular frequency
  • Φ : elektra potencialo
  • Λ : Cosmological constant
  • Ψ : quantum wavefunction
  • Ω : precession angular speed


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