問一個數學名詞

Dirtected numbers are numbers with an PLUS sign or a MINUS sign.
Because on the number line , these numbers have direction ,
so they are called directed numbers.
Natural numbers
The most familiar numbers are the natural numbers, which to some mean the non-negative integers and to others mean the positive integers. In everyday parlance the non-negative integers are commonly referred to as whole numbers, the positive integers as counting numbers.
In the base ten number system, in almost universal use, the symbols for natural numbers are written using ten digits, 0 through 9. An implied place value system, one that increments in powers of ten, is used for numbers greater than nine. Thus, numbers greater than nine have numerals formed with two or more digits. The symbol for the set of all natural numbers is
圖片參考：http://upload.wikimedia.org/math/e/5/b/e5b2e1e7459ccc17ef8193b7bd6f7aea.png

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Integers
Negative numbers are numbers which are less than zero. They are usually written by indicating their opposite, which is a positive number, with a preceding minus sign. For example, if a positive number is used to indicate distance to the right of a fixed point, a negative number would indicate distance to the left. Similarly, if a positive number indicates a bank deposit, then a negative number indicates a withdrawal. When the negative whole numbers are combined with the positive whole numbers and zero, one obtains the integers
圖片參考：http://upload.wikimedia.org/math/0/b/1/0b100eeff3848a15dbb46291e7fe52ad.png
(German Zahl, plural Zahlen).

2006-10-21 16:47:26 補充：
Beasides , directed numbers usually refers to real numbers

跨某= =

Directed Number = 有向數

那個第只是幾號！

no no no