>>11628964>>11629266108 = 36+36+36 = 36+72.
The top marked green angle is shown as small as it could be which is 36 degrees. The second marked green angle is by definition also 36 degrees, making the complimentary gray marked angle 36 degrees and creating isosceles triangles so the intersection for the lower green line must be the bottom left corner.
If the top marked green angle is as big as it could be (infinitely close to the top corner) then it would be 72 degrees, making the second green angle by definition 72 degrees and the lower green line would intersect the bottom right corner.
Either way, the angle x must be 72 degrees.
Used FreeCAD sketch with constraints to prove it.
