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# Math Sets Help

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## Sets

A set is a collection or group of definable elements or members. Some examples of set elements are:

• points on a line
• instants in time
• individual apples in a basket
• coordinates in a plane
• coordinates in space
• coordinates on a display
• curves on a graph or display
• chemical elements
• individual people in a city
• locations in memory or storage
• data bits, bytes, or characters
• subscribers to a network

If an object or number (call it a) is an element of set A, this fact is written as:

a A

The symbol means ''is an element of.''

## Intersections and Unions

### Set Intersection

The intersection of two sets A and B, written A B, is the set C such that the following statement is true for every element x:

x C if and only if x A and x B

### Set Union

The union of two sets A and B, written A B, is the set C such that the following statement is true for every element x:

x C if and only if x A or x B

## Subsets

A set A is a subset of a set B, written A B, if and only if the following holds true:

x A implies that x B

The symbol is read ''is a subset of.'' In this context, ''implies that'' is meant in the strongest possible sense. The statement ''This implies that'' is equivalent to ''If this is true, then that is always true.''

### Proper Subsets

A set A is a proper subset of a set B, written A B, if and only if the following both hold true:

x A implies that x B
as long as AB

The symbol is read ''is a proper subset of.''

### Disjoint Sets

Two sets A and B are disjoint if and only if all three of the following conditions are met:

A
B
A B =

where denotes the empty set, also called the null set. It is a set that doesn't contain any elements, like a basket of apples without the apples.

### Coincident Sets

Two non-empty sets A and B are coincident if and only if, for all elements x, both of the following are true:

x A implies that x B
x B implies that x A

Practice problems for these concepts can be found at:

Background Math Practice Test

150 Characters allowed

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