The square of the sum of three numbers is equal to the sum of the squares of these three numbers plus twice the product of every two terms. The square of the sum of four numbers is equal to the sum of squares of these four numbers plus twice the product of every two numbers. The square of the sum of several numbers is equal to the sum of the squares of these numbers plus twice the product of every two numbers. Ping method and formula can also be used in real life.
Extension:
I. Sum of squares:
A mathematical term defined as the sum of squares of two or more numbers. Usually it is the sum of squares of some positive integers, and the number of integers can be limited or infinite. Square is an operation, for example, the square of a means a*a, abbreviated as a.
Second, the concept of mathematical formula:
Mathematical formula is an expression method that people find some connection between things in nature and express it in some way. It represents the equal or unequal relationship between the quantities of different things in nature, accurately reflects the internal and external relations of things, and is the basis for us to reach another thing from one thing, so as to better understand the essence and connotation of things.
Third, the characteristics of the wrong formula:
1. claims to be scientific, but it is vague and lacks specific weights and measures.
2. Operation definitions (for example, public variables, objects that belong to or can be checked by outsiders) cannot be used.
3. Can't meet the principle of simplicity, that is, when there are many variables, you can't get the answer in the simplest way.
4. Use ambiguous language and a lot of technical terms to make the article look scientific.
5. Lack of boundary conditions: rigorous scientific theory clearly defines the limited scope and clearly points out when and where the prediction phenomenon is applicable and when and where it is not applicable.
Four, commonly used mathematical formulas
Circumference:
The circumference of a rectangle = (length+width) ×2 = 2(a+b) = (a+b)×2.
Circumference of a square = side length ×4 = 4a