Acenith has been tasked by the Pharaoh with constructing a model of the next pyramid to be built. He wants his scale model to be perfect, but the usual trick of using ropes with length 3, 4, and 5 to make a right angle won't work (as he doesn't have a rope).
However, he does have boards of the following lengths: 2, 3, 5, 9, 10, 12, 15, and 20.
What is the least number of boards he could use (without cutting) to lay out a right angle and ensure that his model looks right for Pharaoh's inspection?