/N / l;"l>t 1 21 



17. Orthogonal projection. The orthogonal projection* f 



;.rinlu ular from 



.t t< tii.- linr. In the figure, M in th- j.r..j.-.-u,,n 

 .I// 'I'!.'- pro f ft segmeut PQ of ft 



line upon another line AB. is that part of tin* second line 

 in tin- ; ' tli initial point !' tin- eg- 



iiirnt t th projection of the terminal point <f tin- sr^m 

 Thus MN ia the projection of PQ upon ^i#, and NM is the 



ction of 0<P U P ^^ 



Tli.' length of the projection can easily be expressed in 



Irn^th of tli- .s.-Ljmriit ami tin- an^h- \\liirh it 



makes with the line upon which the se^m N>J60l6d| fur 



the projeftion of a tegment of a line upon another linf 

 if f, t ' it* length by the cosine of the angle 



' it make* > 



\ line made up of \*rt* PQ. QJ*' .\\hieh 



are si .litYeivm ihrectious, is a broken line : 



i.ui of a ln-okrii line upon anv line is the 

 algebraic >uin of the projc, : i-.irts upon the same 



II if i, r, unlew otherwiM uted, pr&etio* will be understood to 

 mean orfAot/owa/ prvjttt. 



