Davies, Charles, 1798-1876 · New York and Chicago, A. S. Barnes and company · leaf 53
THEOREM XIX The cJiOrd of an arc of sixty degrees is equal to the radius ofthe circle. et AEB be an arc of sixty degreesand AB its chord: then will AB be equalto the radius of the circle. For, draw the radii CB and CA.Then, since the angle ACB is at thecentre, it will be measured by the arcAEB:… … BOOK II. 53 Of the Circle. follows that the sum of the two angles A and B will be equalto one hundred and twenty degrees. But the triangle CA Bis isosceles: hence, the angles at the base are equal (Bk. I.1 h. vi): hence, each angle is equal to sixty degrees, andconsequently, the side AB is equal to…
Geometry · Plane trigonometry
Internet Archive · Library of Congress · Public Domain Mark 1.0. Free to use for anything.
![An illustration from Vnderweysung der Messung : mit dem Zirkel vn[d] Richtscheyt in Linien, Ebnen vnnd gantzen Corporen (1525)](https://img.insideoutlibrary.com/img/200/ia-vnderweysungderm00drer-57-112.webp)
