Special right triangle are in the ratio 1 : 2 : 3 and respectively measure 30° (), 60° (), and 90° (). The sides are in the ratio 1 : : 2. The proof of this fact is clear using trigonometry. The geometric proof is: The 30°–60°–90° triangle is the only right triangle whose angles are in an arithmetic progression. The proof of this fact is simple and follows on from the fact that if "α", , are the angles in the progression then the sum of the angles = 180°. After dividing by 3, the angle must be 60°. The right angle
Facial Angles (Camper) for Philipp von Stosch's "Pierres Antiques Gravées". The facial angles of Moors and Kalmyks was calculated to be 70 degrees, and that of a European 80 degrees. The original report of these lectures in the proceedings of the literature society is listed as one of the 1000 most important texts in the Canon of Dutch Literature. Facial Angles (Camper) Facial Angles refers to the content of two lectures on this subject by the Amsterdam professor of anatomy Petrus Camper on the 1st and 8 August in 1770 to the Amsterdam Drawing Academy called the "Teken-akademie". Camper was a competent artist