Elements of geometry : containing the first six books of Euclid, with a supplement on the quadrature of the circle, and the geometry of solids : to which are added, Elements of plane and spherical geometry (1826)
Playfair, John, 1748-1819, Euclid · Philadelphia : Marot & Walter · leaf 186
XIX. THEOR. Two straight lines not in the same plane being given in posi-tion, to draw a straight line perpendicular to them both. Let AB and CD be the given lines, which are not in the same Slane; it is required to draw a straight line which shall be perpeu-ieular both to AB and CD.1h AB take any… … GK and let this plane meet CDinH; from H drawHK perpendicu-lar to AB; and HK is the line required. Tlirough H, draw HGparallel to AB. Then, since HK and GE, which are in the same plane, are both atright angles to the straight line AB, they are parallel to oiie another.And because the lines HG. HD…
Euclid's Elements · Geometry · Trigonometry
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