Davies, Charles, 1798-1876 · New York and Chicago, A. S. Barnes and company · leaf 48
e double the angle at the circumference. Cor. 2. If two angles at the circumference stand on equalarcH thev will be equal to each other. BOOK II. 47 Of the Circle • THEOREM II. A11 angles at the circumference, which, stand upon the same arcare equal to each other. Let the angles BAC, BDC, BFC,… … B THEOREM X. An angle in a semicircle, is a right angle. Let ABBC be a semicircle : then willevery angle, as B, B, inscribed in it, bea right angle. For, each angle is measured by half jthe semic^rcumference ADC, that is, by aquadiant, which measures a right anglefBk I. Th. i. Cor. 2). D B
Geometry · Plane trigonometry
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