Aldis, W. Steadman (William Steadman), 1839-1928 · Cambridge [Eng.] Deighton, Bell, and co.; London, G. Bell and sons · leaf 31
be p, and Z, m, n its direc-tion-cosines. Let P be any point in the plane. Then sinceOD is perpendicular to the plane it is perpendicular to PD.Hence OD is the projection of OP on OD. Draw PM parallel to Oz to meet the plane of xy in M,and MN ])arallel to Oy to meet Ox in N. Then the projec-tion of… … a relation which is satisfied by the co-ordinates of any pointin the plane, and therefore the equation of the plane. If the plane is perpendicular to one of the co-ordinateplanes, as for instance that of xy, OD will lie in that plane,and we have ?i = 0. Hence the equation in that case be-comes Ix +…
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