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 177
F is equal to the angle ABC and theyare both in the same plane, which is impos>sible: therefore the straight line BC is notabove the plane in which are BD and BE:Wherefore the three straight lines BC, BD,BE are inone and the same plane. There-fore, if three straight lines, &c. Q. E. D. PROP.… … OF GEOMETRY. BOOK II. irr Let them meet the plane in the points B, D. Draw DE at riarhtangles to DB, in the plane BDE, and let E beany point in it: Join AB, AD, EB. BecauseABB is a ri^ht angle, AB + BE= (47. 1.)AE**, and because BDE is a right angle. BE*=BD^ + DE»; therefore AB + BD^ + OE* =AE3;…
Euclid's Elements · Geometry · Trigonometry
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