Legendre, A. M. (Adrien Marie), 1752-1833, Brewster, David, Sir, 1781-1868, Davies, Charles, 1798-1876 · New York, Wiley & Long · leaf 82
or, let O be the point where AB andCD meet. In the triangle OEF, the lineAC being drawn parallel to the base EF,we shall have OE : AE : : OF : CF, orOE : OF : ; AE : CF. In the triangleOGII, we shall likewise have OE : EG: : OF : FII,orOE : OF : : EG : FH.And by reason of the common ratio OE :OF,… … BOOK IV. 83 PROPOSITION XVI. THEOREM. Conversely, if two sides of a triangle are cut proportiunally hy astraight line, this straight line will be parallel to the third side. In llie tiiaiigle ABC, let the line I)E be drawn, makingAD : DB : : AE : EC : then will DE be parallel to BC. For, if DE is…
Trigonometry · Geometry
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