Proposition: Prop. 13.10: Square on Side of Regular Pentagon inscribed in Circle equals Squares on Sides of Hexagon and Decagon inscribed in sa

(Proposition 10 from Book 13 of Euclid's “Elements”)

If an equilateral pentagon is inscribed in a circle then the square on the side of the pentagon is (equal to) the (sum of the squares) on the (sides) of the hexagon and of the decagon inscribed in the same circle$^\dag$ * Let $ABCDE$ be a circle. * And let the equilateral pentagon $ABCDE$ have been inscribed in circle $ABCDE$. * I say that the square on the side of pentagon $ABCDE$ is the (sum of the squares) on the sides of the hexagon and of the decagon inscribed in circle $ABCDE$.