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 36
. XXVII. THEOR. If a straight line falling upon two other straight linesmakes the alternate angles equal-to one another, these twostraight lines are parallel. Let the straight line EF, which falls upon the two straight lines AB,CD make the alternate angles AEF, EFD equal to one another; ABis… … OF GEOMETRY. BOOK I. 35 i(s exterior ansfle AEF is greater (16. 1.) than the interior and oppo-site angle EFG: but it isalso equal to it, which isimpossible; therefore, ABand CD being produced,<lo not meet towards B,D. In like manner it maybedemonstrated that theydo not meet towards A,C; but…
Euclid's Elements · Geometry · Trigonometry
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