# Homework Help: Find the domain of the function

1. Sep 9, 2008

### kebstein

hi this is my first time here. i have just been admitted to the university of the gambia last month. i have a problem with this question. please i need help

find the domain
f is such that x maps to 1 all over the squareroot of x2-10x+12.

2. Sep 9, 2008

### CompuChip

Re: functions

I assume you meant
$$f: x \mapsto \frac{1}{\sqrt{x^2 - 10x + 12}}$$.

What is the definition of domain? How would you go about finding it?

Last edited: Sep 9, 2008
3. Sep 9, 2008

### kebstein

Re: functions

yeah this is what i meant,

Last edited: Sep 9, 2008
4. Sep 9, 2008

### CompuChip

Re: functions

OK, so can you show us some attempt / ideas you had (no matter how stupid you think they are)? You completely ignored the template that pops up when posting a question, but it's there for a good reason. We are not too good at guessing what you do and don't know; moreover the idea is we just help you find the answer yourself, instead of just giving it to you.

5. Sep 9, 2008

### HallsofIvy

Re: functions

you were asked before, what is the definition of "domain". If you know that definition, please tell us what it is. If you don't, look it up! You can't hope to do problems involving words you don't know!

6. Sep 11, 2008

### kebstein

Re: functions

there is an error in my first question. it should
f: x mapsto frac{1}{\\sqrt{x^2 - 10x + 21}')

7. Sep 11, 2008

### kebstein

Re: functions

i think i have to factorize x2-10+21
x2-3x-7x+21
x(x-3)-7(x-3)
(x-3) (x-7)

x-3 is greater than or equal to 0 and x-7 is greater than or equal 0
there for x is greater than or equal to 3 and x is greater than or equal to7

then Df = [3; 7]

is this correct

Last edited: Sep 11, 2008