math
9th Grade - types of numbers

9th grade lesson

1 - Types of numbers


Different types

Numbers can be classified into different sets. Here are the most useful sets:

entiers naturels is the set of natural numbers. They are numbers without point and greater than zero.
fraction
are natural numbers.
fraction
aren't natural numbers.


natural numbers is the set of relative numbers, or integers. They are numbers without point.
integers
are integers.
numbers
aren't integers.


decimal numbers is the set of decimal numbers. They are numbers with a finite number of figures after the point.
decimal numbers
are decimal numbers.
numbers
aren't decimal numbers.


rational numbers is the set of rational numbers. They are the numbers you can write in the form of fractions.
rational numbers
are rational numbers.
numbers
aren't rational numbers.


real numbers is the set of real numbers. Every number you know is a real number.

positive real numbers is the set of positive numbers.

negative real numbers is the set of negative numbers.

real numbers without zero is the set of numbers but without zero.

The number -4 belongs to the set of relative numbers. You can also write : math symbol. The same way, math symbol, and
.



Intervals

[2;3] is the set of all numbers between 2 and 3.
[4;5[ is the set of all numbers between 4 and 5, except 5.
]-2;1[ is the set of all numbers between -2 and 1, except -2 and 1.
line and intervals


Union of sets

The union of two sets, is the set of numbers that belong to the first set added to the set of numbers that belong to the second set.
You symbolize the union by a capital u : U.
[1;2]U[4;5]
[0;4]U[2;5] = [0;5]
]-4;-2]U]-3;-1] = ]-4 ; -1]

intervals union


Intersection of intervals

The intersection of two intervals is the set of the numbers that belong to the first and the second one.:

intervals

The last result is the empty set, that is the set without any number in it.



>>> Absolute values lesson >>>


Types of numbers

lesson, problems