Spanton, J. Humphrey (John Humphrey) · London, Macmillan and Co., Limited; New York, The Macmillan Company · leaf 91
escribe a semicircle and divide itinto nine equal parts (Prob. 48). Draw the lines B4 and B7.Then the three angles 7BC,4B7, and 4BA are in theproportion of 2 : 3 : 4. Thesum of the three angles areequal to two right angles,because a semicircle con-tains 180° ; so they mustbe the three angles of… … 120. This problem illustrates an important principle in proportion. Take a triangle ABC, the sides of which shall bear acertain ratio. For example, let AB : BC as 2 : i. Pro- D duce AB to D, and bisect the / ^, angles ABC and DBC bylines meeting AQ and ACproduced in H and E.Bisect the line HE in…
Geometrical drawing · Design · Drawing
Internet Archive · Wellesley College Library · Public Domain Mark 1.0. Free to use for anything.
![An illustration from Divina proportione : opera a tutti glingegni perspicaci e curiosi necessaria oue ciascun studioso di philosophia: prospettiua pictura sculptura: architectura: musica: e altre mathematice: suavissima: sotile: e admirabile doctrina consequira: e delecterassi: co[n] varie questione de secretissima scientia (1509)](https://img.insideoutlibrary.com/img/200/ia-divinaproportion00paci-85-121.webp)
