Whats the domain?????

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August 20th 2008, 05:54 PM
sadieann

Whats the domain?????

http://webwork.math.wvu.edu/webwork2...9a5f89b581.png
August 20th 2008, 06:16 PM
arbolis

The domain is all the $x$ that make $x(x-18)>0$ .
August 20th 2008, 06:19 PM
sadieann

I know that..but i need the domain in interval notation of that function
August 20th 2008, 06:25 PM
Chris L T521

Quote:

Originally Posted by arbolis

The domain is all the $x$ that make $x(x-18)>0$ .

Quote:

Originally Posted by sadieann

I know that..but i need the domain in interval notation of that function

Well, if you know this is the case, then for what values of x is this inequality true? Just solve the inequality. Its fairly straightforward. Once you solve the inequality, the intervals become pretty obvious.

--Chris
August 20th 2008, 06:25 PM
arbolis

Ok. Note that $x(x-18)$ vanishes when x equals 0 or 18. Note also that $y=x(x-18)=x^2-18x$ is an equation of a parabola with a global minimum. That mean that $x(x-18)\geq 0$ when $x \in (-\infty,0]$ U $[18,+\infty,)$ , that's your domain.
EDIT: I'm sorry in my first post, it should be "The domain is all the $x$ that make $x(x-18)\geq 0$ ."
August 20th 2008, 06:38 PM
sadieann

Thank you so much man.
August 20th 2008, 06:43 PM
arbolis

A pleasure to help. I understand you were in a rush but when you have time, try to understand what I did and ask us if you don't understand. Good luck.

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