Types of Real Numbers
Date: 8/16/96 at 21:1:48 From: Louie M Subject: The Types of Real Numbers I would like to know all the types of real numbers. Thanks! Chris
Date: 8/30/96 at 16:56:13 From: Doctor James Subject: Re: The Types of Real Numbers There are many, many types of real numbers. I'll tell you about a few here. The most general division of the real numbers is the division between the rational numbers and the irrational numbers. A rational number is defined to be any number that can be expressed as p/q, where p and q are both integers (we'll come to them in a second) and q does not equal 0. You can recognize a rational number because it either has only a finite number of decimal places (or no decimal places at all!), or the decimal places repeat themselves. That is, the following are all rational numbers: 348100 78.33954001 3.333333333... .0000123232323232323... But you can make some numbers that don't follow those rules. That is, you could have a number like 1.01001000100001000001... which goes on forever, but never repeats itself. These are called irrational numbers, and most aren't that pretty. Two of the more famous ones are pi = 3.14159... e = 2.718... You can subdivide the rationals further, in many ways. Here are some ways: negative numbers, 0, and positive numbers integers and non-integers. Integers are, roughly speaking, numbers with no decimal points, like 4 or 10 or -3788882 or 0. I say roughly speaking, because 9/9 is an integer, and so is 3.00. In these cases, it's important to be equal to something without a decimal point. Non-integers are everything else (irrational numbers are also non-integers). Then there are whole numbers and natural numbers (also called counting numbers). Natural numbers are positive integers, like 1, 2, 3, 4... Whole numbers are natural numbers and 0. There are also something called imaginary or complex numbers, which are outside of the real numbers. These come about when you ask questions like, 'what is the square root of -4?' The fundamental unit of the imaginary numbers is i, which is defined to be the number such that i^2 = -1. Thus, the square root of -4 is 2i (can you see why?). Imaginary numbers are a very interesting subject, which if you keep on in math you'll learn about soon enough. Hope this helps! -Doctor James, The Math Forum Check out our web site! http://mathforum.org/dr.math/ PS. In a branch of math called number theory you learn a lot about various types of numbers, such as prime numbers and perfect numbers and square numbers and triangular numbers...
Search the Dr. Math Library:
Ask Dr. MathTM
© 1994-2015 The Math Forum