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Square root of a function

  1. Sep 16, 2012 #1
    1. The problem statement, all variables and given/known data

    I have the function H^2 + 12756H and I want to find the domain and range of it's square root algebraically.


    2. Relevant equations


    3. The attempt at a solution

    I understand y= √(H^2 + 12756H) is undefined if H^2 + 12756H < 0, however I dont get how to find its domain and range using algebra. Maybe someone can help me.
     
    Last edited: Sep 16, 2012
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  3. Sep 16, 2012 #2

    SammyS

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    Can you solve for H2 + 12756H = 0 ?

    If you graph y = H2 + 12756H you get a continuous graph. H2 + 12756H cannot change sign without going through zero.

    All of that should help you.
     
  4. Sep 16, 2012 #3
    I understand how to find the domain and range of the root function by looking at the original graph, however my question is can it be done algebraically, if so how?

    And no I dont believe you can solve for H with 0 = h^2 + 12756h algebraically only with quadratic formula. The point of this post is to find out the easiest way to solve this sort of thing for domain, and would it be finding x-intercepts and deriving your domain of the root from that ?
     
    Last edited: Sep 16, 2012
  5. Sep 16, 2012 #4

    SammyS

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    How purely algebraic do you want the solution to be?

    Yes, it can be done!
     
  6. Sep 19, 2012 #5

    HallsofIvy

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    H^2+ 12756H= H(H+ 12756)< 0 and the product of two numbers is negative if and only if the numbers are of opposite sign.
    So either H< 0 and H+ 12756> or H> 0 and H+ 12756< 0.
    (Only one of those is actually possible.)
     
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