Euclid's Proposition 2
- Erik Tou
Here we see the construction that Euclid uses to "copy" one line segment (here, BC) onto the end of a given point (A). The full proof can be found online at: http://aleph0.clarku.edu/~djoyce/java/elements/bookI/propI2.html
Note that in order to construct the equilateral triangle ABD, Euclid must appeal to Proposition 1 (which itself requires the construction of two circles of equal radius).