The circumference of a circle is equal to π times the diameter of the circle. It is also equal to 2 times π times the radius of the circle. (generally, π is not specified, π=3. 14)C: indicates the circumference of a circle; D: indicates the diameter of the circle; R: indicates the radius of the circle.

Second, Fourier transform:

Fourier transform means that functions that meet certain conditions can be expressed as trigonometric functions (sine and/or cosine functions) or linear combinations of their integrals. In different research fields, Fourier transform has many different variants, such as continuous Fourier transform and discrete Fourier transform. Firstly, Fourier analysis is proposed as a tool for thermal process analysis.

Third, the de Broglie equation:

De Broglie thinks that particles and waves have the same characteristics (that is, they can be regarded as the same in the quantitative description of the material world), so he assumes that their efficiency is equivalent: MC 2 = HV' Because the actual particles do not move at the speed of light in vacuum, De Broglie multiplies the group velocity v (velocity) by the phase velocity u instead of the square of c (light) to get mvu=hv'.

Fourth, Schrodinger equation:

Schrodinger equation (Schrodinger? Schrodinger equation, also known as Schrodinger wave equation, is the basic equation and hypothesis in quantum mechanics proposed by Austrian physicist Schrodinger.

It is a second-order partial differential equation established by combining the concept of matter wave with wave equation, which can describe the movement of microscopic particles. Every microscopic system has its own Schrodinger equation. By solving the equation, we can get the specific form of wave function and the corresponding energy, so as to understand the properties of micro-system.

Five, the mass-energy equation:

Mass-energy equation is an equation describing the equivalent relationship between mass and energy. In classical physics, mass and energy are two completely different concepts, and there is no definite equivalent relationship between them. Objects of a certain mass can have different energies. The concept of energy is also limited, and there are kinetic energy and potential energy in mechanics. In the special theory of relativity, the concept of energy has been generalized, and there is a definite equivalence relationship between mass and energy. If the mass of the object is m, the corresponding energy is E=mc? .

Six, Pythagorean theorem:

Pythagorean theorem is a basic geometric theorem, which means that the sum of the squares of two right angles of a right triangle is equal to the square of the hypotenuse. In ancient China, right-angled triangles were called Pythagorean Theorem, the smaller right-angled side was a hook, the other longer right-angled side was a chord, and the hypotenuse was a chord, so this theorem was called Pythagorean Theorem, and some people called it quotient height theorem.

There are about 500 ways to prove Pythagorean theorem, and Pythagorean theorem is one of the most proven theorems in mathematics. Pythagorean theorem is one of the important mathematical theorems discovered and proved by human beings in the early days. It is one of the most important tools to solve geometric problems with algebraic ideas, and it is also one of the ties of the combination of numbers and shapes.

Seven, Newton's second law:

The common expression of Newton's second law of motion is that the acceleration of an object is directly proportional to the acting force, inversely proportional to the mass of the object, and directly proportional to the reciprocal of the mass of the object; The direction of acceleration is the same as that of acting force. This law was put forward by isaac newton in his book Mathematical Principles of Natural Philosophy 1687. Newton's second law of motion, the first and third laws together constitute Newton's law of motion, and the basic law of motion in classical mechanics is expounded.

Eight, Euler formula:

In complex variable function, e (ix) = (cos x+isinx) is called Euler formula, e is the base of natural logarithm, and I is imaginary unit. In topology, on any regular spherical graph, if R is used to record the number of regions, V is used to record the number of vertices, and E is used to record the number of boundaries, then R+ V- E= 2, which is euler theorem? It was first proved by Descartes in 1640, and later independently proved by Euler in 1752. We call it euler theorem, and some people abroad call it Descartes theorem.

Nine, Maxwell's equations:

Maxwell equations are a set of partial differential equations established by British physicist james clerk maxwell in19th century, which are used to describe the relationship among electric field, magnetic field, charge density and current density. It consists of four equations: Gauss's law describing how electric charge produces electric field, Gauss's law describing how electric current and time-varying electric field produce magnetic field, Maxwell-Ampere's law describing how time-varying magnetic field produces electric field, Faraday's law describing how time-varying magnetic field produces electric field.

X. 1+ 1:

It is a conjecture put forward by the German mathematician Goldbach (Goldbach conjecture). Any even number ≥6 can be expressed as the sum of two odd prime numbers. Any odd number ≥9 can be expressed as the sum of no more than three odd prime numbers.