1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Stupid Mistake?

  1. Jan 23, 2004 #1
    If f(x) = square root of x and g(x) = x + 1, then:

    1. What is f+g(x)?
    2. Domain of f+g(x)?
    3. What is f(g(x))?
    4. What is the domain of f(g(x))?

    I put:

    1. square root of x + x + 1
    2. x >= 0
    3. square root of x + 1
    4. All real numbers?

    Thanks.
     
  2. jcsd
  3. Jan 23, 2004 #2
    Number 4 depends on whether you "allow" complex numbers or not...
     
  4. Jan 23, 2004 #3

    ahrkron

    User Avatar
    Staff Emeritus
    Gold Member

    Just to make sure, do you mean
    sqrt(x) + x+1
    or
    sqrt(x+x+1)
    ??

    OK (as long as you are only talking about reals)

    Again, use parentheses.

    Nope. Example: x = -3.
     
  5. Jan 23, 2004 #4

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    In #2 you had already asserted that the domain of g+h (x)= √(x)+ x+1 is x>= 0 so you are talking about real valued functions of a real value (you can't take the square root of a negative number).

    In #4, then, f(g(x))= &radic(x+1), you must have x+1>= 0.
     
  6. Jan 23, 2004 #5
    Ug I hate it when I make mistakes like this! I knew how to do it and then when I'm under pressure I mess up everytime! Ack. So frustrating...lol... Oh well, just a quiz grade. Maybe I can make it up somehow...lol...
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Stupid Mistake?
  1. Stupid Equation (Replies: 4)

  2. Hidden mistake (Replies: 4)

  3. Math mistakes (Replies: 4)

  4. Mistake in proof. (Replies: 5)

  5. Stupid question (Replies: 33)

Loading...