Ancient Greek
Section 19
Scholia in Euclidem, Scholia in Euclidis optica (scholia vetera) 19
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19. Πρὸς ὀρθὰς γωνίας ἴσαι p. 12, εἰ γάρ τις εἴποι, ὡς ἡ ΗΓ κάθετός ἐστι πρὸς τὴν Γ∠, ὡσαύτως δὲ καὶ ἡ ΖΒ πρὸς τὴν ΒΑ, δῆλον ἔσται τὸ ἄτοπον. εἰ γὰρ ἡ ὑπὸ ΗΓ∠ γωνία ὀρθή, καὶ ἡ ὑπὸ Β ὀρθὴ ἔσται.