# Algebra/Closure

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 Algebra Closure

## Closure

Closure is a property that is defined for a set of numbers and an operation. This Wikipedia article gives a description of the closure property with examples from various areas in math. As an Algebra student being aware of the closure property can help you solve a problem. For instance a problem might state "The sum of two whole numbers is 24." With practice you will be able to see that the possible set of numbers will be either all odd (e.g. (1,23),(3,21), ... etc.) or all even (e.g. (2,22), (4,20), ... etc.). The problem might not explicitly state the idea of whole numbers. It might state that two sides of a square sum to 24. If you remember working a problem like this before you know that the sides of a square need to be equal and you divide by two. The author of the problem might want to be trickier and say that two sides of an equilateral triangle sum to 24 and then ask for the perimeter of the triangle. In this case you might want to write the equation ${\displaystyle 3x=p}$ for the perimeter of an equilateral triangle. This might make it easier for you to see that again you just need to divide 24 by 2 to find the length of one side and plug it into the equation.

## Exercises For Closure

Consider each statement and try to come up with an example that proves it is false. If you can do that write down your example and mark the answer false. Otherwise mark the answer true.
Natural Numbers

1

Addition is closed under the Natural Numbers.

 true false

2

Subtraction is closed under the Natural Numbers.

 true false

3

Multiplication is closed under the Natural Numbers.

 true false

4

Division is closed under the Natural Numbers.

 true false

5

Exponentiation is closed under the Natural Numbers.

 true false

6

Roots are closed under the Natural Numbers.

 true false
Whole Numbers

7

Addition is closed under the Whole Numbers.

 true false

8

Subtraction is closed under the Whole Numbers.

 true false

9

Multiplication is closed under the Whole Numbers.

 true false

10

Division is closed under the Whole Numbers.

 true false

11

Exponentiation is closed under the Whole Numbers.

 true false

12

Roots are closed under the Whole Numbers.

 true false
Integers

13

Addition is closed under the Integers.

 true false

14

Subtraction is closed under the Integers.

 true false

15

Multiplication is closed under the Integers.

 true false

16

Division is closed under the Integers.

 true false

17

Exponentiation is closed under the Integers.

 true false

18

Roots are closed under the Integers.

 true false
Rational Numbers

19

Addition is closed under the Rational Numbers.

 true false

20

Subtraction is closed under the Rational Numbers.

 true false

21

Multiplication is closed under the Rational Numbers.

 true false

22

Division is closed under the Rational Numbers.

 true false

23

Exponentiation is closed under the Rational Numbers.

 true false

24

Roots are closed under the Rational Numbers.

 true false
Irrational Numbers

25

Addition is closed under the Irrational Numbers.

 true false

26

Subtraction is closed under the Irrational Numbers.

 true false

27

Multiplication is closed under the Irrational Numbers.

 true false

28

Division is closed under the Irrational Numbers.

 true false

29

Exponentiation is closed under the Irrational Numbers.

 true false

30

Roots are closed under the Irrational Numbers.

 true false
Real Numbers

31

Addition is closed under the Real Numbers.

 true false

32

Subtraction is closed under the Real Numbers.

 true false

33

Multiplication is closed under the Real Numbers.

 true false

34

Division is closed under the Real Numbers.

 true false

35

Exponentiation is closed under the Real Numbers.

 true false

36

Roots are closed under the Real Numbers.

 true false