A treatise on surveying and navigation: uniting the theoretical, the practical, and the educational features of these subjects (1852)
Robinson, Horatio N[elson], 1806-1867. [from old catalog] · Cincinnati, J. Ernst · leaf 64
s as follows. The sine of 30° is half radius ;making the radius unity, equation (1) gives£-f-cos.2 30°= 1: whence cos.2 30°=f or cos. 30°=£«/3; From (32) we have, sin.a=A/1—cos- %« 2Making 2a=30°, then sin. 15°=(^—i>/§)2=0.25881904 From (31) we have, cos.c^A/i+cos- 2« 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=sin.2a, CG=cos.2a,DI=sm. a, AD=2 sin. a,CI =±=cos. a, DB —2D 0=2 cos.…
Surveying · Navigation
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