# Thread: Need help with this

1. ## Need help with this

How can i possibly approach 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:
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.