Euclid's Elements Book 1: Proposition 2
Proposition 2: “From a given point, to draw a straight line equal to a given finite straight line”. In other words, given a point
Proof.
Let the given point be
Use postule 1 to draw a line between
Next, use proposition 1 to draw an equilateral triangle from the drawn line
Next, describe a circle with center
Extend the line DB all the way till intersects the circle at
Now describe another circle with center
Extend the line DA until it intersects the circle at
The claim is that
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