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Find k such that the line is tangent to the graph

  1. May 20, 2004 #1
    I'm not sure what they are looking for here.

    Find k such that the line is tangent to the graph of the funtion

    Function: x^2-kx Line: 4x-9

    Just need a little push in the right direction.
     
  2. jcsd
  3. May 20, 2004 #2

    arildno

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    Hints:
    You must find 2 features:
    a) A point in common between the graphs of your function and your line.
    b) That the slope of the function at that point equals the line's slope

    This is a system of two equations!
    Solutions to this system is what you are looking after (a k-value will be one of the numbers in a given solution, a x-value of the point of intersection will be the other number)
     
  4. May 20, 2004 #3
    thanks, I'll give it a shot.
     
  5. May 20, 2004 #4
    A solution that doesn't involve calculus: if the line is supposed to tangent the other function, then the equation 4x - 9 = x^2 - kx may only have one solution. If you solve this for x, what can you say about the discriminant?
     
  6. May 20, 2004 #5
    arildno, did you see your mistake (in the deleted post), or did you remove it in order to not rouse my anger? :wink:
     
  7. May 20, 2004 #6

    arildno

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    That's why I deleted my dumb message..
     
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