Schmall, Charles Nelson. [from old catalog] · New York, D. Van Nostrand company · leaf 298
: M N P Fig. 154. of the parts of that line. — Let the broken line be ACDB,and XX the line on which it is to be projected. Let 6^, 0,, e, be the angles made by AC, CD, DB with XX. Then LP = LM + MN + NP, or, AB cos (9 = AC cos 6^ + CD cos 6., + DB cos 0^. .*., etc. THE POINT 281 … Note. — If any portion of the broken line has a negative direction, itsangle is also negative, and therefore the product of its length by thecosine is always positive. This important principle of projections de-pends on the convention of signs, or the fact that the algebraic length ofa line and the…
Geometry, Analytic
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