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Couple questions

  1. Oct 5, 2004 #1
    I kinda have a question and an answer check... well heres my check.

    Let f(x) = x^2 + x. For any readl number a, let Ty be the y-intrecept of the tangent line to f(a), let Nx and Ny be, respectivly, the x-intercept and y-intercepts of the normal line to f(a). SHow that a = 0 is the only value for which the area of the triangle (0,Ny),(0,0),(Nx,0) is equal to the area of triangle (0,Ty),(0,0),(Nx,0).

    to attack this problem i decided since the triangles both have side (0,0),(Nx,0) in common i could just find the equations of the tangent and normal line, find the intercepts of the tangent and normal and then set them equal in magnitude. i ended up with a^2 = a/(2a +1) + a^2 + a
    when i solve i get x = 0, x=-1
    it seems to work out when i plot the graphs for x = -1...
    but in my question it says show that a = 0 is the only possible value, am i drawing it wrong or is my prof missing something? ty

    question #2...

    this should be an easy question...

    f(x) = x/|x| at x = 0;

    the derivative do not exist, explain why. There is a skip ?

    Can the definitions be modified(slightly) so that the derviative does exist at this point, if so calc the derivative. if no explain why. i need help on this question :|
     
  2. jcsd
  3. Oct 5, 2004 #2

    arildno

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    Question 2:
    Draw the function on a piece of paper, and you'll see.
     
  4. Oct 5, 2004 #3
    If anyone can help im in major need :|
     
  5. Oct 6, 2004 #4

    HallsofIvy

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    A function has to be continuous before it can be differentiable!
     
  6. Oct 6, 2004 #5
    yah felt kinda silly by asking for help on #2, well for anyone who was wondering...for #1 my prof was wrong. He said he made a mistake after i confronted him about the two values.. Oh well sounds good. ty everyone that helped
     
  7. Oct 6, 2004 #6

    arildno

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    Isn't it great when showing your prof. that he also makes mistakes..:wink:
     
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