A rectangle made of elastic material will be made into a cylinder by joining edges AD and BC. To support the structure, a wire of fixed length L is placed along the diagonal of the rectangle. Find the angle $\displaystyle \theta$ that will result in the cylinder of maximum volume.

see attached picture

thank you very much!

unfortunately i cannot attach a picture

so here is a shot at it...

d._________c

..|............/|

..|........./...|

..|....../......|

..|.../.........|

a|/............|b

theta is angle a, in the triangle cab