Results 1 to 7 of 7

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

  1. #1
    Member
    Joined
    May 2008
    Posts
    112

    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
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Senior Member
    Joined
    Nov 2007
    Posts
    329
    Because in \sqrt{x} x must be greater than or equal to 0 (at least if you want it to be real..)
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    May 2008
    Posts
    112
    Quote Originally Posted by james_bond View Post
    Because in \sqrt{x} x must be greater or equal to 0.
    Can't you have a negative inside a square root?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Senior Member
    Joined
    Nov 2007
    Posts
    329
    Only if you're familiar with complex numbers, see here.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Member
    Joined
    May 2008
    Posts
    112
    Ahh, thanks!
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Member
    Joined
    May 2008
    Posts
    112
    Hmmm, another question...how come this is different then?

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

    Answer: (-infinity, -4) U (4, infinity)
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Senior Member
    Joined
    Nov 2007
    Posts
    329
    |a| = \begin{cases} a, & \mbox{if } a \ge 0 \\ -a, & \mbox{if } a < 0. \end{cases}
    Can you solve it now?
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Finding domain of function
    Posted in the Pre-Calculus Forum
    Replies: 7
    Last Post: November 12th 2011, 06:16 AM
  2. Finding the domain of a function.
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: November 7th 2011, 06:44 PM
  3. Replies: 4
    Last Post: September 18th 2010, 05:16 AM
  4. Finding the domain of this function?
    Posted in the Algebra Forum
    Replies: 3
    Last Post: September 11th 2008, 02:16 AM
  5. Finding the domain of a function
    Posted in the Pre-Calculus Forum
    Replies: 6
    Last Post: January 30th 2008, 03:51 PM

Search Tags


/mathhelpforum @mathhelpforum