Legendre, A. M. (Adrien Marie), 1752-1833, Brewster, David, Sir, 1781-1868, Davies, Charles, 1798-1876 · New York, Wiley & Long · leaf 128
B D PROPOSITION IV. THEOREM. If a straight line he perpendicular to two straight lines at theirpoint of intersection, it will he perpendicular to the plane ofthose lines. … Let MN be the plane of thetwo Unes BB, CC, and let APbe perpendicular to them attheir point of intersection P ;then will AP be perpendicularto every line of the plane pass-ing through P, and corsequentlyto the plane itself (Def. 1.). Through P, draw in the planeMN, any straight line as PQ,and…
Trigonometry · Geometry
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