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Math Help - Lost in this one, dimensions

  1. #1
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    Lost in this one, dimensions

    Find, correct to five decimal places, the dimensions of the rectangle of largest area that has its base on the x-axis and its other two vertices above the x-axis and lying on the curve y = cos x .

    I have no idea where to begin... I don't even be clear what it wants for the result
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  2. #2
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    My initial approach was to start with

    A = bh = x.cos(x)

    and then evaluate A'=0 to find the points but I got stuck in the process, I missed something or maybe I'm evaluating the wrong area.
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  3. #3
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    Quote Originally Posted by dax918 View Post
    My initial approach was to start with

    A = bh = x.cos(x)

    and then evaluate A'=0 to find the points but I got stuck in the process, I missed something or maybe I'm evaluating the wrong area.
    If "x" is the length of the base, as well as the x-coordinate of a point, then you must have the other vertex as x=0. But their y= cos(0)= 1 so, unless cos(x)= 1, you will not have a rectangle.

    But this problem, as stated, has no solution. Taking the left side at x_0, we can take the right side at x+ 2n\pi having arbitrarily large area. There is NO "largest area".
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