A treatise on surveying and navigation: uniting the theoretical, practical, and educational features of these subjects (1857)
Robinson, Horatio N[elson], 1806-1867. [from old catalog] · Cincinnati, J. Ernst; Toledo, Anderson, Burr, & co. · leaf 62
peration is as follows. The sine of 30° is half radius ;making the radius unity, equation (1) gives^+cos.2 30°= 1 : whence cos.2 30°=f or cos. 30°=^^^ From (32) we have, sin-a^/1-003- 2a 2Making 2a=3Q°, then sin. 15°=(-J—^3)2=0.25881904 From (31) we have, cos.«=a//H^°^1_^ Making 2a=30° as before,… … PLANE TRIGONOMETRY. 59 Being desirous of giving a full exposition of the formation oftable II, we give the following geometrical demonstration of equa-tion 30, by the help of the figure in the margin. Let the arc AD=2aThen DG=sm. 2a, CG=cos.2a,DI = sin. a, AD = 2 sin. a,CI =cos. a, DB=2D 0=2 cos.…
Surveying · Navigation
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![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-124-341.webp)
