# Math Help - Finding domain of this function, don't understand it

1. ## Finding domain of this function, don't understand it

f(x) = x / sqrt(x+4)

x + 4 = 0
x = -4

OK, so the domain can't include -4 BUT why is it all real numbers greater than -4?

Answer: Domain is all real numbers greater than -4

2. Because in $\sqrt{x}$ $x$ must be greater than or equal to 0 (at least if you want it to be real..)

3. Originally Posted by james_bond
Because in $\sqrt{x}$ $x$ must be greater or equal to 0.
Can't you have a negative inside a square root?

4. Only if you're familiar with complex numbers, see here.

5. Ahh, thanks!

6. Hmmm, another question...how come this is different then?

f(x) = x / sqrt( abs(x) - 4 )

Answer: (-infinity, -4) U (4, infinity)

7. $|a| = \begin{cases} a, & \mbox{if } a \ge 0 \\ -a, & \mbox{if } a < 0. \end{cases}$
Can you solve it now?