My Math Forum  

Go Back   My Math Forum > High School Math Forum > Algebra

Algebra Pre-Algebra and Basic Algebra Math Forum


Thanks Tree11Thanks
Reply
 
LinkBack Thread Tools Display Modes
April 4th, 2017, 08:58 PM   #1
Senior Member
 
Joined: Feb 2016
From: seattle

Posts: 370
Thanks: 10

state the domain of the following use set notation and interval notation

state the domain of the following...thanks I am so clueless

f(x)=x
GIjoefan1976 is offline  
 
April 4th, 2017, 09:13 PM   #2
Senior Member
 
Joined: Aug 2012

Posts: 1,620
Thanks: 411

Well that's a good question. What number system are we working in?

All things being equal, you are probably working in the real numbers. The variable $x$ often stands for a real number. So I'd guess that the domain is the reals.

But the function $f(x) = x$ is the identity function that returns whatever value is input to it; and there is an identity function on every set there is. For example there is an identity function on the natural numbers that would typically be denoted as $f(n) = n$. But the use of $x$ or $n$ is only a general convention and can't always be relied on. Maybe $n$ is an integer rather than a natural number.

So the real answer is that you have to supply more information to determine the definitive answer.
Thanks from Joppy and GIjoefan1976
Maschke is offline  
April 4th, 2017, 09:24 PM   #3
Senior Member
 
Joined: Feb 2016
From: seattle

Posts: 370
Thanks: 10

Quote:
Originally Posted by Maschke View Post
Well that's a good question. What number system are we working in?

All things being equal, you are probably working in the real numbers. The variable $x$ often stands for a real number. So I'd guess that the domain is the reals.

But the function $f(x) = x$ is the identity function that returns whatever value is input to it; and there is an identity function on every set there is. For example there is an identity function on the natural numbers that would typically be denoted as $f(n) = n$. But the use of $x$ or $n$ is only a general convention and can't always be relied on. Maybe $n$ is an integer rather than a natural number.

So the real answer is that you have to supply more information to determine the definitive answer.
Hello thanks for your time...I think I saw my teacher use something that looked the pi symbol but had it kinda like this if they were connected TR have you seen this? so would the interval be (-oo,oo) and then the set the symbol for real numbers? he also said not to divide by 0 and don't take the even root of a negative number
GIjoefan1976 is offline  
April 4th, 2017, 10:22 PM   #4
Senior Member
 
Joined: Aug 2012

Posts: 1,620
Thanks: 411

Quote:
Originally Posted by GIjoefan1976 View Post
Hello thanks for your time...I think I saw my teacher use something that looked the pi symbol but had it kinda like this if they were connected TR have you seen this? so would the interval be (-oo,oo) and then the set the symbol for real numbers? he also said not to divide by 0 and don't take the even root of a negative number
$\mathbb R$? That's the real numbers. $(-\infty, ~~\infty)$ is another notation for the real numbers. Sounds like you're working in the real numbers.
Thanks from GIjoefan1976
Maschke is offline  
April 4th, 2017, 10:25 PM   #5
Global Moderator
 
Joined: Dec 2006

Posts: 18,142
Thanks: 1417

The symbol ℝ or $\small\mathbb{R}$ is used to denote the set of all reals.
Thanks from GIjoefan1976
skipjack is offline  
April 4th, 2017, 11:14 PM   #6
Senior Member
 
Joined: Feb 2016
From: seattle

Posts: 370
Thanks: 10

I don't want to people to get upset so not sure what I would look up to find out more but how can these following questions be answered if it seems we don't have anything to plug in for x? so would the square root of x-1 be (-1,oo)?
GIjoefan1976 is offline  
April 4th, 2017, 11:25 PM   #7
Senior Member
 
Joined: Aug 2012

Posts: 1,620
Thanks: 411

Quote:
Originally Posted by GIjoefan1976 View Post
I don't want to people to get upset so not sure what I would look up to find out more but how can these following questions be answered if it seems we don't have anything to plug in for x? so would the square root of x-1 be (-1,oo)?
In order to take the square root of $x - 1$ we must have $x - 1 \geq 0$ or $x \geq 1$. So the domain is $[1, ~\infty)$. Does that make sense?

Also the way you wrote it, we can't tell if you mean $\sqrt{x - 1}$ or $\sqrt{x} - 1$, which is different.

You can write sqrt(x - 1) or sqrt(x) - 1, depending on which one you mean. But writing it out in English without parentheses is ambiguous.
Thanks from Joppy

Last edited by Maschke; April 4th, 2017 at 11:30 PM.
Maschke is offline  
April 4th, 2017, 11:40 PM   #8
Senior Member
 
Joined: Feb 2016
From: seattle

Posts: 370
Thanks: 10

Quote:
Originally Posted by Maschke View Post
In order to take the square root of $x - 1$ we must have $x - 1 \geq 0$ or $x \geq 1$. So the domain is $[1, ~\infty)$. Does that make sense?

Also the way you wrote it, we can't tell if you mean $\sqrt{x - 1}$ or $\sqrt{x} - 1$, which is different.

You can write sqrt(x - 1) or sqrt(x) - 1, depending on which one you mean. But writing it out in English without parentheses is ambiguous.
okay sorry, the way they have it, it is g(x)=sqrt(x-1)
GIjoefan1976 is offline  
April 5th, 2017, 12:42 AM   #9
Senior Member
 
Joined: Aug 2012

Posts: 1,620
Thanks: 411

Quote:
Originally Posted by GIjoefan1976 View Post
okay sorry, the way they have it, it is g(x)=sqrt(x-1)
Do you see why the domain is anything greater than or equal to 1?
Maschke is offline  
April 5th, 2017, 12:49 AM   #10
Senior Member
 
Joined: Feb 2016
From: seattle

Posts: 370
Thanks: 10

Quote:
Originally Posted by Maschke View Post
Do you see why the domain is anything greater than or equal to 1?
thank you for asking, I think I do because the x is positive, and even though it says negative it would still be 1 since it's one space no matter which way we go?
GIjoefan1976 is offline  
Reply

  My Math Forum > High School Math Forum > Algebra

Tags
domain, interval, notation, set, state



Thread Tools
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
How do I express the domain in 'Interval Notation'? elifast Algebra 3 September 20th, 2012 08:21 PM
Find the 'domain' of the function through 'interval notation elifast Algebra 1 September 19th, 2012 02:11 PM
Interval Notation Ambiguity Pyrath Algebra 3 June 23rd, 2012 08:47 AM
Interval Notation mandiimeow Algebra 1 April 19th, 2010 05:32 AM
Set Builder to Interval Notation MathChallenged2010 Algebra 6 March 2nd, 2010 07:41 AM





Copyright © 2017 My Math Forum. All rights reserved.