As here 27. and 12. be like flattes: bicause their sides be in one proportion. For as. 9. is to. 3. so 6 is to. 2. bothe beeyng in triple proportion.
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Master You saie well. And that is the cause why thei be called like: for the likenesse in the proportiō of their sides. Squarelike figures. Although some menne delite more to call them squarelike figures: bicause thei haue some propoerties agreable with square nombers (for as Euclide saieth in his. 8. booke, and. 18. proposition:
Euery twoo nombers, beeyng like flattes, haue one meane nomber betwene theim in proportion. And the one flatte nomber beareth vnto the other flatte double that proportion, that their sides doe.
For declaration of whiche proportion, marke the twoo flatte nombers before: I meane. 27. and. 12. whose sides are in proportion Sesquialter: And the flat nombers themselfes be as 9⁄4. or. 9. to. 4: that is double Sequiquarte. Now doe you double the proportion Sesquialter, and it will make double Sesquiquarte.
Scholar. Thus doe I sette them in order. 3⁄2:3⁄2. And I multiplie the numerators together, and the denominators also. (For I remember, you tolde me before, that proportions are added, as fractions are multiplied) and then will it be. 9⁄4: euen as you saied.
Master. Again Euclide saith in the twenteth proposition of the same booke.
If any nomber stande as a middle nomber inproportion,
