The Math Forum

Ask Dr. Math - Questions and Answers from our Archives
Associated Topics || Dr. Math Home || Search Dr. Math

Old Test Questions Answered

Date: 23 Jan 1995 19:52:49 -0500
From: Cheryl A. Backman
Subject: math questions

Hi there!  I am studying for my course III midterm, which happens to be 
tomorrow.  In reviewing an old chapter test, I've come across two 
questions that I got wrong and don't understand why.  I was wondering if 
you could please help me with this.  Thanks.

        Here they are:

        State the largest possible domain such that the given relation 
     is a function
                x-2           (b)  g(x)= __1___
                                      the square root of x-1

       For part b, there was an "x" and then an arrow with a "g" over it
pointing to the right.  I assumed it was g(x).  Sorry, I couldn't get the 
computer to do that or the square root.

Thanks again,  Michele

Date: 24 Jan 1995 01:29:43 GMT
From: Dr. Math
Subject: Re: math questions

Hello there!

You want to figure out what numbers make sense to plug in
to your functions.  In the first one, which I'll write f(x) = 2/(x-2), you
can pretty much plug in anything, EXCEPT something which would make you 
divide by zero.  So for what value of x is x-2=0?  

You're right about the next problem, which sounds like it was written 
g:x -> 1/Sqrt{x-1}.  It can also be written g(x) = 1/Sqrt{x-1}, and here
you have the same deal.  What numbers can you plug in to this function? 

Well, again, anything that makes sense.  But here it's a little
different.  You still can't divide by zero, but you also can't take the
square root of a negative number.  So you'll have to exclude all the x
that make x-1 negative or zero.

I hope this helps!

-Ken "Dr." Math

Date: 23 Jan 1995 21:30:34 -0500
From: Cheryl A. Backman
Subject: thanks

Dr. Math,
         Thanks again for your response. The explanation made a world of 
Associated Topics:
High School Basic Algebra

Search the Dr. Math Library:

Find items containing (put spaces between keywords):
Click only once for faster results:

[ Choose "whole words" when searching for a word like age.]

all keywords, in any order at least one, that exact phrase
parts of words whole words

Submit your own question to Dr. Math

[Privacy Policy] [Terms of Use]

Math Forum Home || Math Library || Quick Reference || Math Forum Search

Ask Dr. MathTM
© 1994- The Math Forum at NCTM. All rights reserved.