Proposition 12
Construction
To draw a line perpendicular to a given infinite line from a given point not on it.
ἐπὶ τὴν δοθϵῖσαν ϵὐθϵῖαν ἄπϵιρον ἀπὸ τοῦ δοθέντος σημϵίου, ὃ μή ἐστιν ἐπ᾽ αὐτῆς, κάθϵτον ϵὐθϵῖαν γραμμὴν ἀγαγϵῖν.
To a given infinite straight line, from a given point which is not on it, to draw a perpendicular straight line.