Finding domain of function (need an explanation for 2 Qs)

[iwantcalculus]

i need help with finding the domain for a function where there is a square root , here is the picture of such questions :

http://imgur.com/YcqadOe

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!

 

[C. Lee]

let's start with question 35, this is how i try to solve it :

x^2 - 5x > 0

x (x-5) >0

You are correct.

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?

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

 

[Ray Vickson]

i need help with finding the domain for a function where there is a square root , here is the picture of such questions :

http://imgur.com/YcqadOe

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!

Does "pls" mean "please"? Please avoid "text speak" here.

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.

 

[Mark44]

pls help!

As Ray points out, "textspeak" isn't permitted at this site.
From the forum rules (https://www.physicsforums.com/threads/physics-forums-global-guidelines.414380/):

Language:
All posts must be in English. Posts in other languages will be deleted. Pay reasonable attention to written English communication standards. This includes the use of proper grammatical structure, punctuation, capitalization, spacing, and spelling. In particular, "I" is capitalized, there's a space after (but not before) a comma, a period, and other punctuation. Multiple exclamation marks are also discouraged. SMS messaging shorthand ("text-message-speak"), such as using "u" for "you", "please" for "please", or "wanna" for "want to" is not acceptable.

 

[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.