Beman, Wooster Woodruff, 1850-1922, Smith, David Eugene, 1860-1944 · Boston, Ginn & company · leaf 290
parallel projections on any plane. (Suppose,as a special case, that the lines are perpendicular to the plane.) 581. If two lines are at right angles, are their projections on any planealso at right angles ? 582. If two planes are perpendicular to each other, any line perpen-dicular to one of them… … Given ABC, DEF, two lines cut by planes P, Q, R, inpoints A, B, C and 1), E, F. To prove that AB : BC = BE: EF. Proof. 1. Suppose the line GIIF, drawn through F, II ABC,cutting P, Q at G, H, respectively.Then AC, GF determine a plane; also DF, GF. Prop. I, cors. 2, 1 2. .-. AGWBH II CF, and DG II…
Geometry
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