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Need help with level curves

  1. Jul 18, 2008 #1
    1. The problem statement, all variables and given/known data

    Well,I'm having a problem drawing level curves for piecewise functions.
    The problem is, how do I know which value the constant k will hold?

    2. Relevant equations

    The functions is the following:

    f(x,y)=4 if x^2+y^2<=16
    sqrt(32-x^2-y^2) if 16<x^2+y^2<=32

    3. The attempt at a solution

    The solution I've attempted and which I'm not sure it's correct is:
    I've drawn a level curve of level 4,because it's within the domain of f(x,y)(which is ]-infinity;32]) and it's the point where the function changes to the other branch.
    Does this make sense?

    Just another question,to determine the domain of the second "piece" of the function,why do we also use the sqrt(32-x^2-y^2) condition and not only just the if clause?

    Thanks in advance for the reply!
  2. jcsd
  3. Jul 18, 2008 #2
    I don't know if following would help you.

    z = sqrt(32-x^2-y^2) ==> z^2 + x^2+y^2 = (sqrt(32))^2
    this is a sphere.

    first draw level curves for this,

    and then erase all but curves that are between circles with 4 and (sqrt(32))^2
  4. Jul 18, 2008 #3
    What I don't understand is,why do we use the k constant with value 4 specifically?Why couldn't we use other value?
    Also,in the second piece of the function why do we equal sqrt(32-x^2-y^2)=4?Does it have anything to do with the fact that 4 is the point where the function switches to the other branch?
  5. Jul 19, 2008 #4


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    Science Advisor

    Level curves are curves of f(x,y, z)= k for severa; different values of k. Use whatever values of k you like.
  6. Jul 19, 2008 #5
    Do the values of k must be within the range of the function?
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