Is the inclusion symbol: a contains B- then b is a subset of a or equal to a.
True inclusion: A is really included in the proper subset of B-if B = {1, 2}, then A={ 1} or {2} or an empty set.
Operation symbols: such as plus sign (+), minus sign (-), multiplication sign (× or), division sign (÷ or/), union of two sets (∩), intersection (∩), root sign (√), logarithm (log, lg,
Relative symbols: for example, "=" is an equal sign, "≈" is an approximate symbol (that is, approximately equal to), "≦" is an unequal sign, and ">" is a greater than sign. "
"≒" is a similar symbol, "≒" is a complete equal sign, "∨" is a parallel symbol, "∧" is a vertical symbol, "∧" is a proportional symbol (inverse ratio can be expressed by reciprocal relationship) and "∈" is a symbol. "is contained in the symbol;
"?" Does the symbol "|" mean "divisible" (for example, a|b means "A is divisible by B", and? ||b means that R is the greatest power that A can be divisible by B), and any letter such as X and Y can represent an unknown number.
Extended data has two events A and B in a random phenomenon. If any sample point in event A must be in B, it is said that A is contained in B, or B contains A, and it is recorded as A? B or B? A, then the occurrence of event A will inevitably lead to the occurrence of event B.
The relationship between them is active and passive. A containing B means that B is a subset of A, and A containing B means that A is a subset of B. ..
For example, {1, 2,3} contains {1, 2}, but {1, 2} is contained in {1, 2,3}.
Permutation and combination symbol
C combination number
A permutation number
Total number of n elements
R number of elements participating in the selection
! Factorial, such as 5! =5×4×3×2× 1= 120, specify 0! = 1
! ! Half factorial (also called double factorial), for example, 7! ! =7×5×3× 1= 105, 10! ! = 10×8×6×4×2=3840