Elements of geometry and trigonometry. Revised and adapted to the course of mathematical instruction in the United States (1856)
Legendre, A. M. (Adrien Marie), 1752-1833, Davies, Charles, 1798-1876 · New York : A.S. Barnes · leaf 372
entsides of a regular pohjgon^ is equal to the side of die poly-gon multiplied, by tlie cosine of the angle which is obtainedby dividing 360° by twice the number of sides: dte radiusbeiug equal to unity. For, let ABODE be any regularpolygon. Draw the diagonal A (7, andfrom the centre F, draw FG… … 68 MENSUEATION OF SOLIDS. 60° . _.^ ^.^ 360^ AFB = ^^^^, and AFG = CAB - „^^But, in the riglit-angled triangle ABff, we have, o nr\o All = AB cos A = AB cos ^ (Trig., Th. 6). Remark 1.—When the polygon in question is the equi-lateral triangle, the diagonal becomes a side, and conse-quently, half…
Geometry · Trigonometry
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