ξζ΄.
Ἐὰν τρίγωνον δεδομένην ἔχῃ γωνίαν, ᾧ μεῖζον δύνανται αἱ τὴν δεδομένην γωνίαν περιέχουσαι πλευραὶ ὡς μία τοῦ ἀπὸ τῆς λοιπῆς, ἐκεῖνο τὸ χωρίον πρὸς τὸ τρίγωνον λόγον ἕξει δεδομένον.
ἔστω τρίγωνον τὸ ΑΒΓ δεδομένην ἔχον γωνίαν τὴν ὑπὸ τῶν ΒΑΓ· λέγω, ὅτι, ᾧ μεῖζόν ἐστι τὸ ἀπὸ συναμφοτέρου τῆς ΒΑΓ τοῦ ἀπὸ τῆς ΒΓ, ἐκεῖνο τὸ χωρίον πρὸς τὸ ΑΒΓ τρίγωνον λόγον ἔχει δεδομένον.
διήχθω γὰρ ἐπʼ εὐθείας τῆς ΑΒ εὐθεῖα ἡ ΑΔ,
καὶ κείσθω τῇ ΑΓ ἴση ἡ ΑΔ, καὶ ἐπιζευχθεῖσα ἡ ΔΓ διήχθω ἐπὶ τὸ Ε, καὶ ἤχθω διὰ τοῦ Β τῇ ΑΓ παρ- 1 άλληλος ἡ ΒΕ. καὶ ἐπεὶ ἴση ἐστὶν ἡ ΑΔ τῇ ΑΓ, ἴση ἄρα ἐστὶ καὶ ἡ ΔΒ τῆ ΒΕ. καὶ διῆκταί τις ἡ ΒΓ· τὸ ἄρα ὑπὸ τῶν ΔΓΕ μετὰ τοῦ ἀπὸ τῆς ΒΓ ἴσον ἐστὶ τῷ ἀπὸ τῆς ΒΔ. ἴση δὲ ἡ ΔΑ τῇ ΑΓ· τὸ ἄρα
ἀπὸ συναμφοτέρου τῆς ΒΑΓ ἴσον ἐστὶ τῷ ὑπὸ τῶν ΔΓΕ μετὰ τοῦ ἀπὸ τῆς ΒΓ· ὥστε τὸ ἀπὸ συναμφο- τέρου τῆς ΒΑΓ τοῦ ἀπὸ τῆς ΒΓ μεῖζόν ἐστι τῷ ὑπὸ τῶν ΔΓΕ.
καὶ κείσθω τῇ ΑΓ ἴση ἡ ΑΔ, καὶ ἐπιζευχθεῖσα ἡ ΔΓ διήχθω ἐπὶ τὸ Ε, καὶ ἤχθω διὰ τοῦ Β τῇ ΑΓ παρ- 1 άλληλος ἡ ΒΕ. καὶ ἐπεὶ ἴση ἐστὶν ἡ ΑΔ τῇ ΑΓ, ἴση ἄρα ἐστὶ καὶ ἡ ΔΒ τῆ ΒΕ. καὶ διῆκταί τις ἡ ΒΓ· τὸ ἄρα ὑπὸ τῶν ΔΓΕ μετὰ τοῦ ἀπὸ τῆς ΒΓ ἴσον ἐστὶ τῷ ἀπὸ τῆς ΒΔ. ἴση δὲ ἡ ΔΑ τῇ ΑΓ· τὸ ἄρα
ἀπὸ συναμφοτέρου τῆς ΒΑΓ ἴσον ἐστὶ τῷ ὑπὸ τῶν ΔΓΕ μετὰ τοῦ ἀπὸ τῆς ΒΓ· ὥστε τὸ ἀπὸ συναμφο- τέρου τῆς ΒΑΓ τοῦ ἀπὸ τῆς ΒΓ μεῖζόν ἐστι τῷ ὑπὸ τῶν ΔΓΕ.
λέγω δή, ὅτι τοῦ ὑπὸ τῶν ΔΓΕ πρὸς τὸ ΑΒΓ
τρίγωνον λόγος ἐστὶ δοθείς.
τρίγωνον λόγος ἐστὶ δοθείς.
ἐπεὶ γὰρ δοθεῖσά ἐστιν ἡ ὑπὸ τῶν ΒΑΓ γωνία, καὶ ἡ ἐφεξῆς ἄρα ἡ ὑπὸ τῶν ΔΑΓ ἐστι δοθεῖσα. ἔστι δὲ καὶ ἑκατέρα τῶν ὑπὸ τῶν ΑΔΓ, ΔΓΑ δοθεῖσα· ἡμίσειαι γάρ εἰσι τῆς ὑπὸ τῶν ΒΑΓ· [δέδοται γὰρ ἡ
ὑπὸ ΒΑΓ·] δέδοται ἄρα τὸ ΔΑΓ τρίγωνον τῷ εἴδει· λόγος ἄρα ἐστὶ τῆς ΔΑ πρὸς τὴν ΔΓ δοθείς· ὥστε καὶ τοῦ ἀπὸ τῆς ΑΔ πρὸς τὸ ἀπὸ τῆς ΔΓ λόγος ἐστὶ δοθείς. καὶ ἐπεὶ ὡς ἡ ΒΑ πρὸς τὴν ΑΔ, οὕτως ἡ ΕΓ πρὸς τὴν ΓΔ, ἀλλʼ ὡς μὲν ἡ ΒΑ πρὸς ΑΔ, οὕτως
τὸ ὑπὸ ΒΑ, ΑΔ πρὸς τὸ ἀπὸ ΑΔ, ὡς δὲ ἧ ΕΓ πρὸς ΓΔ, οὕτως τὸ ὑπὸ τῶν ΕΓ, ΓΔ πρὸς τὸ ἀπὸ ΓΔ, καὶ ὡς ἄρα τὸ ὑπὸ τῶν ΒΑ, ΑΔ πρὸς τὸ ἀπὸ τῆς ΔΑ, οὕτως τὸ ὑπὸ τῶν ΕΓΔ πρὸς τὸ ἀπὸ τῆς ΓΔ· καὶ ἐναλλάξ, ὡς ἄρα τὸ ὑπὸ τῶν ΒΑΔ πρὸς τὸ ὑπὸ τῶν
ΕΓΔ, οὕτως τὸ ἀπὸ τῆς ΑΔ πρὸς τὸ ἀπὸ τῆς ΔΓ. λόγος δὲ τοῦ ἀπὸ τῆς ΑΔ πρὸς τὸ ἀπὸ τῆς ΔΓ δο- θείς· λόγος ἄρα καὶ τοῦ ὑπὸ τῶν ΒΑΔ πρὸς τὸ ὑπὸ τῶν EΓΔ δοθείς. ἴση δὲ ἡ ΔΑ τῇ ΑΓ· λόγος ἄρα 2 τοῦ ὑπὸ τῶν ΒΑΓ πρὸς τὸ ὑπὸ τῶν ΕΓΔ δοθείς. τοῦ δὲ ὑπὸ τῶν ΒΑΓ πρὸς τὸ ΑΒΓ τρίγωνον λόγος ἐστὶ δοθείς, διὰ τὸ δοθεῖσαν εἶναι τὴν ὑπὸ τῶν ΒΑΓ καὶ τοῦ ὑπὸ τῶν ΔΓΕ ἄρα πρὸς τὸ ΑΒΓ λόγος ἐστὶ
δοθείς. καί ἐστι τὸ ὑπὸ ΔΓΕ ᾧ μεῖζόν ἐστι τὸ ἀπὸ συναμφοτέρου τῆς ΒΑΓ τοῦ ἀπὸ τῆς ΒΓ· ᾧ ἄρα μεῖζόν ἐστι τὸ ἀπὸ συναμφοτέρου τῆς ΒΑΓ τοῦ ἀπὸ τῆς ΒΓ, ἐκεῖνο τὸ χωρίον πρὸς τὸ τρίγωνον λόγον ἕξει δεδομένον.
ὑπὸ ΒΑΓ·] δέδοται ἄρα τὸ ΔΑΓ τρίγωνον τῷ εἴδει· λόγος ἄρα ἐστὶ τῆς ΔΑ πρὸς τὴν ΔΓ δοθείς· ὥστε καὶ τοῦ ἀπὸ τῆς ΑΔ πρὸς τὸ ἀπὸ τῆς ΔΓ λόγος ἐστὶ δοθείς. καὶ ἐπεὶ ὡς ἡ ΒΑ πρὸς τὴν ΑΔ, οὕτως ἡ ΕΓ πρὸς τὴν ΓΔ, ἀλλʼ ὡς μὲν ἡ ΒΑ πρὸς ΑΔ, οὕτως
τὸ ὑπὸ ΒΑ, ΑΔ πρὸς τὸ ἀπὸ ΑΔ, ὡς δὲ ἧ ΕΓ πρὸς ΓΔ, οὕτως τὸ ὑπὸ τῶν ΕΓ, ΓΔ πρὸς τὸ ἀπὸ ΓΔ, καὶ ὡς ἄρα τὸ ὑπὸ τῶν ΒΑ, ΑΔ πρὸς τὸ ἀπὸ τῆς ΔΑ, οὕτως τὸ ὑπὸ τῶν ΕΓΔ πρὸς τὸ ἀπὸ τῆς ΓΔ· καὶ ἐναλλάξ, ὡς ἄρα τὸ ὑπὸ τῶν ΒΑΔ πρὸς τὸ ὑπὸ τῶν
ΕΓΔ, οὕτως τὸ ἀπὸ τῆς ΑΔ πρὸς τὸ ἀπὸ τῆς ΔΓ. λόγος δὲ τοῦ ἀπὸ τῆς ΑΔ πρὸς τὸ ἀπὸ τῆς ΔΓ δο- θείς· λόγος ἄρα καὶ τοῦ ὑπὸ τῶν ΒΑΔ πρὸς τὸ ὑπὸ τῶν EΓΔ δοθείς. ἴση δὲ ἡ ΔΑ τῇ ΑΓ· λόγος ἄρα 2 τοῦ ὑπὸ τῶν ΒΑΓ πρὸς τὸ ὑπὸ τῶν ΕΓΔ δοθείς. τοῦ δὲ ὑπὸ τῶν ΒΑΓ πρὸς τὸ ΑΒΓ τρίγωνον λόγος ἐστὶ δοθείς, διὰ τὸ δοθεῖσαν εἶναι τὴν ὑπὸ τῶν ΒΑΓ καὶ τοῦ ὑπὸ τῶν ΔΓΕ ἄρα πρὸς τὸ ΑΒΓ λόγος ἐστὶ
δοθείς. καί ἐστι τὸ ὑπὸ ΔΓΕ ᾧ μεῖζόν ἐστι τὸ ἀπὸ συναμφοτέρου τῆς ΒΑΓ τοῦ ἀπὸ τῆς ΒΓ· ᾧ ἄρα μεῖζόν ἐστι τὸ ἀπὸ συναμφοτέρου τῆς ΒΑΓ τοῦ ἀπὸ τῆς ΒΓ, ἐκεῖνο τὸ χωρίον πρὸς τὸ τρίγωνον λόγον ἕξει δεδομένον.
Data. Euclid. ed. Johan Ludvig Heiberg, ed. Heinrich Menge. United States. 2016.
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