What makes you say that? I'm not an expert. Accurate geometry or not, the pyramids are pretty cool. What about them means it couldn't have been trial and error?
About halfway up, however, the angle of incline decreases from over 51 degrees to about 43 degrees, and the sides rise less steeply, causing it to be known as the Bent Pyramid. The change in angle was probably made during construction to give the building more stability