§12.prop.4#1ἐὰν ὦσι δύο πυραμίδες ὑπὸ τὸ αὐτὸ ὕψος τριγώνους ἔχουσαι βάσεις, διαιρεθῇ δὲ ἑκατέρα αὐτῶν εἴς τε δύο πυραμίδας ἴσας ἀλλήλαις καὶ ὁμοίας τῇ ὅλῃ καὶ εἰς δύο πρίσματα ἴσα, ἔσται ὡς ἡ τῆς μιᾶς πυραμίδος βάσις πρὸς τὴν τῆς ἑτέρας πυραμίδος βάσιν, οὕτως τὰ ἐν τῇ μιᾷ πυραμίδι πρίσματα πάντα πρὸς τὰ ἐν τῇ ἑτέρᾳ πυραμίδι πρίσματα πάντα ἰσοπληθῆ.
If there are two pyramids of equal height having triangular bases, and each of them is divided into two pyramids equal to one another and similar to the whole and into two equal prisms, then as the base of the one pyramid is to the base of the other pyramid, so will all the prisms in the one pyramid be to all the prisms, equal in number, in the other pyramid.
ἔστωσαν δύο πυραμίδες ὑπὸ τὸ αὐτὸ ὕψος τριγώνους ἔχουσαι βάσεις τὰς ΑΒΓ, ΔΕΖ, κορυφὰς δὲ τὰ Η, Θ σημεῖα, καὶ διῃρήσθω ἑκατέρα αὐτῶν εἴς τε δύο πυραμίδας ἴσας ἀλλήλαις καὶ ὁμοίας τῇ ὅλῃ καὶ εἰς δύο πρίσματα ἴσα· λέγω, ὅτι ἐστὶν ὡς ἡ ΑΒΓ βάσις πρὸς τὴν ΔΕΖ βάσιν, οὕτως τὰ ἐν τῇ ΑΒΓΗ πυραμίδι πρίσματα πάντα πρὸς τὰ ἐν τῇ ΔΕΖΘ πυραμίδι πρίσματα ἰσοπληθῆ.
Let there be two pyramids of equal height having triangular bases ABG, DEZ, and vertices the points H, Q, and let each of them be divided into two pyramids equal to one another and similar to the whole and into two equal prisms; I say that, as the base ABG is to the base DEZ, so are all the prisms in the pyramid ABGH to all the prisms, equal in number, in the pyramid DEZQ.
ἐπεὶ γὰρ ἴση ἐστὶν ἡ μὲν ΒΞ τῇ ΞΓ, ἡ δὲ ΑΛ τῇ ΛΓ, παράλληλος ἄρα ἐστὶν ἡ ΛΞ τῇ ΑΒ καὶ ὅμοιον τὸ ΑΒΓ τρίγωνον τῷ ΛΞΓ τριγώνῳ.
For since BX is equal to XG, and AL to LG, therefore LX is parallel to AB and the triangle ABG is similar to the triangle LXG.
διὰ τὰ αὐτὰ δὴ καὶ τὸ ΔΕΖ τρίγωνον τῷ ΡΦΖ τριγώνῳ ὅμοιόν ἐστιν.
For the same reason, the triangle DEZ is also similar to the triangle RFZ.
καὶ ἐπεὶ διπλασίων ἐστὶν ἡ μὲν ΒΓ τῆς ΓΞ, ἡ δὲ ΕΖ τῆς ΖΦ, ἔστιν ἄρα ὡς ἡ ΒΓ πρὸς τὴν ΓΞ, οὕτως ἡ ΕΖ πρὸς τὴν ΖΦ. καὶ ἀναγέγραπται ἀπὸ μὲν τῶν ΒΓ, ΓΞ ὅμοιά τε καὶ ὁμοίως κείμενα εὐθύγραμμα τὰ ΑΒΓ, ΛΞΓ, ἀπὸ δὲ τῶν ΕΖ, ΖΦ ὅμοιά τε καὶ ὁμοίως κείμενα τὰ ΔΕΖ, ΡΦΖ. ἔστιν ἄρα ὡς τὸ ΑΒΓ τρίγωνον πρὸς τὸ ΛΞΓ τρίγωνον, οὕτως τὸ ΔΕΖ τρίγωνον πρὸς τὸ ΡΦΖ τρίγωνον· ἐναλλὰξ ἄρα ἐστὶν ὡς τὸ ΑΒΓ τρίγωνον πρὸς τὸ ΔΕΖ, οὕτως τὸ ΛΞΓ πρὸς τὸ ΡΦΖ τρίγωνον.
And since BG is double of GX, and EZ of ZF, therefore, as BG is to GX, so is EZ to ZF. And on BG, GX have been described similar and similarly situated rectilineal figures ABG, LXG, and on EZ, ZF similar and similarly situated figures DEZ, RFZ. Therefore, as the triangle ABG is to the triangle LXG, so is the triangle DEZ to the triangle RFZ; therefore, alternately, as the triangle ABG is to the triangle DEZ, so is the triangle LXG to the triangle RFZ.
ἀλλʼ ὡς τὸ ΛΞΓ τρίγωνον πρὸς τὸ ΡΦΖ τρίγωνον, οὕτως τὸ πρίσμα, οὗ βάσις μὲν τὸ ΛΞΓ τρίγωνον, ἀπεναντίον δὲ τὸ ΟΜΝ, πρὸς τὸ πρίσμα, οὗ βάσις μὲν τὸ ΡΦΖ τρίγωνον, ἀπεναντίον δὲ τὸ ΣΤΥ· καὶ ὡς ἄρα τὸ ΑΒΓ τρίγωνον πρὸς τὸ ΔΕΖ τρίγωνον, οὕτως τὸ πρίσμα, οὗ βάσις μὲν τὸ ΛΞΓ τρίγωνον, ἀπεναντίον δὲ τὸ ΟΜΝ, πρὸς τὸ πρίσμα, οὗ βάσις μὲν τὸ ΡΦΖ τρίγωνον, ἀπεναντίον δὲ τὸ ΣΤΥ. ὡς δὲ τὰ εἰρημένα πρίσματα πρὸς ἄλληλα, οὕτως τὸ πρίσμα, οὗ βάσις μὲν τὸ ΚΒΞΛ παραλληλόγραμμον, ἀπεναντίον δὲ ἡ ΟΜ εὐθεῖα, πρὸς τὸ πρίσμα, οὗ βάσις μὲν τὸ ΠΕΦΡ παραλληλόγραμμον, ἀπεναντίον δὲ ἡ ΣΤ εὐθεῖα.
But as the triangle LXG is to the triangle RFZ, so is the prism of which the base is the triangle LXG, and the opposite the triangle OMN, to the prism of which the base is the triangle RFZ, and the opposite the triangle STY; therefore also, as the triangle ABG is to the triangle DEZ, so is the prism of which the base is the triangle LXG, and the opposite the triangle OMN, to the prism of which the base is the triangle RFZ, and the opposite the triangle STY. And as the aforesaid prisms are to one another, so is the prism of which the base is the parallelogram KBXL, and the opposite the straight line OM, to the prism of which the base is the parallelogram PEFR, and the opposite the straight line ST.
καὶ τὰ δύο ἄρα πρίσματα, οὗ τε βάσις μὲν τὸ ΚΒΞΛ παραλληλόγραμμον, ἀπεναντίον δὲ ἡ ΟΜ, καὶ οὗ βάσις μὲν τὸ ΛΞΓ, ἀπεναντίον δὲ τὸ ΟΜΝ, πρὸς τὰ πρίσματα, οὗ τε βάσις μὲν τὸ ΠΕΦΡ, ἀπεναντίον δὲ ἡ ΣΤ εὐθεῖα, καὶ οὗ βάσις μὲν τὸ ΡΦΖ τρίγωνον, ἀπεναντίον δὲ τὸ ΣΤΥ. καὶ ὡς ἄρα ἡ ΑΒΓ βάσις πρὸς τὴν ΔΕΖ βάσιν, οὕτως τὰ εἰρημένα δύο πρίσματα πρὸς τὰ εἰρημένα δύο πρίσματα.
Therefore also the two prisms, both that of which the base is the parallelogram KBXL, and the opposite the straight line OM, and that of which the base is the triangle LXG, and the opposite the triangle OMN, are to the prisms, both that of which the base is the parallelogram PEFR, and the opposite the straight line ST, and that of which the base is the triangle RFZ, and the opposite the triangle STY. Therefore also, as the base ABG is to the base DEZ, so are the two aforesaid prisms to the two aforesaid prisms.