Euclid's Elements Book 2: Proposition 4, Squaring a Sum

Check out my new website: www.EulersAcademy.org This is the fourth proposition in Euclid's second book of The Elements. This proposition starts with a line that is randomly cut. The square created by the whole line is equal to the sum of the squares on the two cut portions plus twice the rectangle contained by the two segments of the line.