Math Symbols The Most Valuable and Important Symbols For Set Notation In Use:
"Union of Sets"
Background  why math symbols are used. . .
Symbols are a concise way of giving lengthy instructions related to
numbers and logic.
Math Symbols are an invention, not a discovery. They are a
communication tool. Symbols are used to eliminate
the need to write long, plain language instructions to describe
calculations and other processes.
The most valuable, most frequently used Symbols in mathematics . . .
The most important, most frequently used Symbols for Set Notation
are listed below.
Symbols for Set Notation  click symbol
To See
All Symbols
click here
Math Symbol for the "Union of Sets" 
D A means combine Set "D" with Set "A":
(1)
Every element (without exception) contained in Set "D" is combined with every element present in Set "A".
And . . .
(2)
If Set "D" and Set "A" have any elements which are the same, that element is listed only once in the combined set.
Example 1:
, Set A: A = {a, b, c, d}
Set D: D = {e, f}
. . .
The "Union" of Set "D" and Set "A" produces a new set which contains all the elements of both sets: a, b, c, d, e, f
D A = {a, b, c, d, e, f}
Example 2:
, Set B: B = {1, 3, 9, 11, 13, 14}
Set E: E = {1, 3, 9, 11}
. . .
Both Set "E" and Set "B" contain some of the same elements: 1, 3, 9, 11. These elements will only be listed once in the new, combined set.
E B = {1, 3, 9, 11, 13, 14}
Note: When both SETS contain the same element, that element is listed only once in the new, combined set.
Example 3:
, Set C: C = {dog, horse, bird,
rabbit, cat}
Set F: F = {cat, rabbit}
. . .
Both Set "F" and Set "C" list the following elements in a different order: rabbit, cat
F C = {dog, horse, bird,
rabbit, cat}
Note: the elements within a SET can be listed in any order.
