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Thread: Need help with this

  1. #1
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    Question Need help with this

    Need help with this-capture.png

    How can i possibly approach this?

    Thanks in advance.
    Last edited by DaDuFFF; Jun 20th 2018 at 09:49 AM.
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  2. #2
    MHF Contributor MarkFL's Avatar
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    Re: Need help with this

    Years ago, I worked a similar problem, where the lower left corner was brought over to the right edge of the paper, and the paper is smoothed flat creating a crease of length $\displaystyle L$. This is how I labeled the diagram:

    Need help with this-creaselength2.jpg
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  3. #3
    Member Walagaster's Avatar
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    Re: Need help with this

    I have relabeled your figure (click to enlarge):
    Need help with this-fold.jpg
    Notice that the two green triangles are similar. You have $x^2 + t^2 = y^2$ and from the similar triangles you have $\frac t 8 = \frac x r$. Put that $t$ in the first equation and use the Pythagorean theorem to get $r$ from the lower green triangle and put that in. Then you will have an equation for $y$ in terms of $x$ which you can solve for the critical value for $x$. It will come out surprisingly nice.
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