|Book I Proposition 44|
the straight line HF falls upon the parallels AH, EF,
the angles AHF, HFE are equal to two right angles. [I.29]
the angles BHG, GFE are less than two right angles;
and straight lines produced indefinitely from angles less than two right angles meet; [Post.5]
therefore HB, GB, when produced, will meet.
Let them be produced and meet at K;
through the point K
let KL be drawn parallel to either EA or FH [I.31]
let HA, GB be produced to the points L, M.
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