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Homework Help: Increasing and Decreasing Functions (max/min)

  1. Feb 28, 2010 #1
    1. The problem statement, all variables and given/known data

    Find a > 0 so that the curves y = sin ax and y = cos ax intersect at right angles (let them intersect at (x0, y0)).


    2. The attempt at a solution

    Thinking about the unit circle, if theta equals pi/4, then sin theta and cos theta would intersect at right angles at the point (1/sqrt2, 0). Does this imply that sin ax0 = cos ax0? I don't know where to go from here. This problem is at the end of a section that concerned what I can learn about the graph of a function from the first derivative of the function. However, I don't see how the derivatives of the above functions can help me here. I would greatly appreciate a walk-through.
     
  2. jcsd
  3. Feb 28, 2010 #2
    you know one thing if they intersect at right angle, the multiplication of their slope should be negative 1.
    say
    m1=3
    m2=-1/3
    that means that they are perpendicular

    Now, what do derivatives give you ?

    I'm not sure if this works, but you should try
     
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