Here's something I noticed the other day. I draw 3 slabs. All of them measure, when horizontal, 7200mm in length.
I take the second slab, and edit the corners, putting in a dz1 and dz2 to give me a 45 degree angle.
I take the third slab, rotate it 45 degrees, and extend it until it's a similar length to the second one. Not perfect, but in the neighborhood.
So, I have 3 slabs, 2 of them should be about 10 meters long.