유클리드 원론 13권 (Euclid Elements XIII)
Propositions Proposition 1 If a straight line is cut in extreme and mean ratio, then the square on the greater segment added to the half of the whole is five times the square on the half. Proposition 2 If the square on a straight line is five times the square on a segment on it, then, when the double of the said segment is cut in extreme and mean ratio, the greater segment is the remaining part ..