Finding the domain of radical, rational, polynomial fcns  TOPIC_SOLVED

Quadratic equations and inequalities, variation equations, function notation, systems of equations, etc.

Finding the domain of radical, rational, polynomial fcns

Postby tdavis on Wed Aug 12, 2009 6:58 pm

I was wondering if I did this part of my homework correctly. Thanks your input would be greatly appreciated. :)

State the domain of the following:

f(x)=sqrt x+4
domain= x >=0

:) g(x)=(2x+1)/(x-7)
domain= all numbers x different form 0

h(x)=3x^2+5x-3
domain = all real numbers

l(x)=2x+3
domain = all real numbers

e) m(x)=3/(x^2+7)
domain = all numbers x different from 0
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Postby stapel_eliz on Wed Aug 12, 2009 9:30 pm

To learn, in general, how to find domains of functions, try here. :wink:

For the square root function, I'm not sure from your formatting quite what the function is, so I cannot comment on the correctness of your answer.

For the polynomial functions, yes, the domain is always "all x".

For the rational functions, you need to find the value(s) of x which would cause division by zero. The value zero itself is not usually the x-value of interest.... :oops:
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Re: Finding the domain of radical, rational, polynomial fcns  TOPIC_SOLVED

Postby QM deFuturo on Thu Aug 13, 2009 1:08 am

tdavis wrote:I was wondering if I did this part of my homework correctly. Thanks your input would be greatly appreciated. :)

State the domain of the following:

:) g(x)=(2x+1)/(x-7)
domain= all numbers x different form 0


e) m(x)=3/(x^2+7)
domain = all numbers x different from 0


Well, as they say, you're "getting warmer", but not quite there. You want to make sure the denominator of a fraction is never zero, this is true. However, if x = 0 in either of these functions, does that make the denominator zero? If not, what value of x *would* make the denominator zero? THAT is the value you need to exclude from the domain.

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