What does c mean?

The upper right corner of the mathematical symbol C is 1 and the lower right corner is 4, indicating the combination in mathematics. 4 in the lower right corner represents the total number, and 1 in the upper right corner represents the extraction number, and one of the four is extracted. c？ =4÷ 1=4。

Combination: Generally speaking, taking m(m≤n) elements from n different elements as a group is called the combination of taking m elements from n different elements. The total number of all these combinations is called the combination number, and the calculation formula of this combination number is:

The combination obtained by repeatedly extracting M elements from N-ary set A is essentially an M-ary subset of A. ..

The properties of the combination number formed by taking out M different elements from N different elements at one time are as follows:

Using these two properties, we can simplify the calculation of combination number and prove the problems related to combination number.

C stands for combination.

C is 3 in the upper right corner and 5 in the lower right corner, that is to say, how many permutations and combinations of three things are selected from five things (in no particular order)?

Calculation method: 5! /3! *(5-3)! = 1*2*3*4*5/ 1*2*3* 1*2= 10

Along any two sides, greater than the third side.

That is, the combination of three numbers selected from five numbers is 10, minus the invalid (3,4,7)1;

Adding 5*4=20 isosceles triangle and subtracting 2 (3,3,6) (3,3,7) is invalid; There are five equilateral triangles; A * * * has 9+ 18+5=32.