T H E E L E M E N T S |
Book IV Proposition 5 | |
Let the straight lines AB, AC be bisected at the points D, E, [I.10] and from the points D, E let DF, EF be drawn at right angles to AB, AC; they will then meet within the triangle ABC, or on the straight line BC, or outside BC. First let them meet within at F, and let FB, FC, FA be joined. |
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