# Thread: Finding domain of a function!

1. ## Finding domain of a function!

Hey,

Im in high school and im having real bad trouble with this math question.. Its finite math and im learning about linear equations.

Right now im learning about f(x) equations..

I just wanted to see if any of you knew how i would go about this question? Im not sure how to find the domain, heres the question:

"A certain pollutant is being removed from a small lake. Let t be the number of days from the beginning of the removal process and
f(t)= 50(1 - t/120) be the number of parts per million of this pollutant in the water. Find the domain of the function and sketch its graph throughout the domain."

Thanks!!!!

2. For $f(t)= 50\left(1 - \frac{t}{120}\right)$ what values can t take?

Or maybe it might be eaiser to ask yourself are there any values t cannot take?

3. Thats the thing i dont know what values i can use for t... if t is the number of days how do i find a domain if there is no number of days given?

Do i just pick a random number of days, substitute it for t, and work out the graph?

Thanks

4. You question is what values are you 'allowed' to pick for t? Is there any values that you could pick for t that defy logic or mathematical laws?

5. I would say any negative number for t would be incorrect because if t = the number of days the least amount of days would be zero, is that right?

How would i go about putting that into a formula?

6. Originally Posted by Hustla
I would say any negative number for t would be incorrect because if t = the number of days the least amount of days would be zero, is that right?

How would i go about putting that into a formula?
Hi Hustla,

Formula!?! You can represent the domain using interval or set-builder notation for all t values greater than or equal to zero.

$D=\{t|t \ge 0\}$ or $D=[0, +\infty)$

7. Actually as I understand the domain will be $D = \{t|0\le t\le t_f\}$ where $\,t_f$ is the time at which all of the pollutant has been removed.