Developable ruled surfaces and Bezier curves axe widely used in Computer Aided Geometric Deisgn (CAGD). A ruled surface is a surface generated by sweeping a line through space, or more specifically, sweeping a line along a directrix curve. A developable ruled surface is a surface where the surface normal at all points along a given ruling is constant. If the generators and directrix curve of a developable ruled surface are known, operations with these surfaces and designs of them are much simplified.