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 176
. If two planes cut one another, their common section is astraight line. Let two planes AB, BC cnt one an-other, and let 3 and D be two points in theline of their common section. From B toD draw the straight line BO; and becausethe points B and 0 are in the plane AB,the straight line BO is in that… … PROP. IV. THEOR, If a straight line stand at right angles to each of twostraight lines in the point of their intersection, it will alsobe at right angles to the plane in which these lines are. Let the straight line AB stand at right angles to each of the straightlines EF, CD in A, the point of…
Euclid's Elements · Geometry · Trigonometry
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