Proposition 11
Construction
To cut a given line segment into two pieces so that the rectangle contained by the whole and one of the pieces equals the square of the remaining piece.
τὴν δοθϵῖσαν ϵὐθϵῖαν τϵμϵῖν ὥστϵ τὸ ὑπὸ τῆς ὅλης καὶ τοῦ ἑτέρου τῶν τμημάτων πϵριϵχόμϵνον ὀρθογώνιον ἴσον ϵἶναι τῷ ἀπὸ τοῦ λοιποῦ τμήματος τϵτραγώνῳ.
To cut a given straight line so that the rectangle contained by the whole and one of the segments is equal to the square on the remaining segment.