# Homework Help: Finding domain of function (need an explanation for 2 Qs)

1. Sep 6, 2015

### iwantcalculus

• Homework problem moved from a technical forum section
i need help with finding the domain for a function where there is a square root , here is the picture of such questions :

please see the picture, there are two questions in it, 35 and 37
let's start with question 35, this is how i try to solve it :

x^2 - 5x > 0

x (x-5) >0

x>0 and x-5>0 so the other answer is x>5

what to do after getting x>0 and x>5, are they even right?

the real answer is: (-infinity, 0)u(5,infinity)

pls help!

2. Sep 6, 2015

### C. Lee

You are correct.

You should re-think about what conditions x should satisfy for x(x-5) to be greater than 0.

3. Sep 7, 2015

### Ray Vickson

Anyway, $x(x-5) > 0$ does NOT imply that $x>0$ and $x > 5$. (Note that if you know $x > 5$ you already know that $x > 0$, so you don't need to list it as a separate condition.)

More precisely: the inequality $x(x-5) > 0$ means that both $x$ and $x-5$ are nonzero and have the same sign. They do not need to be > 0.

4. Sep 7, 2015

### Staff: Mentor

As Ray points out, "textspeak" isn't permitted at this site.

5. Sep 7, 2015

### RJLiberator

For question #37, consider what must occur:

You cannot have a negative under the square root. So we know that p must be 0 or greater than 0.

Now, use that same philosophy and the condition to fully solve the problem.