Schmall, Charles Nelson. [from old catalog] · New York, D. Van Nostrand company · leaf 298
, 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 cosine of its angle always have the same sign. 7. Angle between… … Fig. 156. Then, the projection of OP^ on OP2 = projection of the broken line ONMP^ on OP2. p^ cos 0 = ON cos ttg + MN cos /?2 + MP^ cos y^= (p^ cos ttj) COS ttg + (pi cos j8.) cos ^2+ (p^ COS yj COS y2 282 ANALYTICAL GEOMETRY [since the co-ordinates of P^ are the projections of ^o^ on theaxes]. .-.…
Geometry, Analytic
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