If as the whole (of a number) is to the whole (of another), so a (part) taken away (is) to a (part) taken away,then the remainder will also be to the remainder as the whole (is) to the whole.
Let the whole AB be to the whole CD as the (part) taken away AE (is) to the (part) taken away CF. I say that the remainder EB is to the remainder FD as the whole AB (is) to the whole CD.
If as the whole (of a number) is to the whole (of another), so a (part) taken away (is) to a (part) taken away,then the remainder will also be to the remainder as the whole (is) to the whole.
Let the whole AB be to the whole CD as the (part) taken away AE (is) to the (part) taken away CF. I say that the remainder EB is to the remainder FD as the whole AB (is) to the whole CD.(For) since as AB is to CD, so AE (is) to CF, thus which(ever) part, or parts, AB is of CD, AE is also the same part, or the same parts, of CF [Def. 7.20]. Thus, the remainder EB is also the same part, or parts, of the remainder FD that AB (is) of CD [Props. 7.7, 7.8].Thus, as EB is to FD, so AB (is) to CD [Def. 7.20]. (Which is) the very thing it was required to show.