Legendre, A. M. (Adrien Marie), 1752-1833, Brewster, David, Sir, 1781-1868, Davies, Charles, 1798-1876 · New York, Wiley & Long · leaf 56
Let AB, CD, be two chords intersectingeach other at E : then will the angleAEC, or DEB, be measured by half ofAC + DB. Draw AF parallel to DC : then willthe arc DF be equal to A( (Prop. X.) ;and the angle FAB equal to the angleDEB (Book I. Prop. XX, Cor. 3.). Butthe angle FAB is measured by half… … PROPOSITION XX. THEOREM. The angle formed by two secants, is measured by half the diffe-rence of the arcs included between its sides. Let AB, AC, be tw^o secants : thenwill the angle BAC be measured byhalf the difference of the arcs BECand DF. Draw DE parallel to AC : then willthe arc EC be equal…
Trigonometry · Geometry
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