BOOK V. PROPOSITIONS.
PROPOSITION I.
If there be any number of magnitudes whatever which are,
respectively,
equimultiples of any magnitudes equal in multitude,
then,
whatever multiple one of the magnitudes is of one,
that multiple also will all be of all.
Let any number of magnitudes whatever
AB,
CD be respectively equimultiples of any magnitudes
E,
F equal in multitude; I say that, whatever multiple
AB is of
E, that multiple will
AB,
CD also be of
E,
F.
For, since
AB is the same multiple of
E that
CD is of
F, as many magnitudes as there are in
AB equal to
E, so many also are there in
CD equal to
F.
Let
AB be divided into the magnitudes
AG,
GB equal to
E, and
CD into
CH,
HD equal to
F; then the multitude of the magnitudes
AG,
GB will be equal to the multitude of the magnitudes
CH,
HD.
Now, since
AG is equal to
E, and
CH to
F, therefore
AG is equal to
E, and
AG,
CH to
E,
F.
For the same reason
GB is equal to
E, and
GB,
HD to
E,
F; therefore, as many magnitudes as there are in
AB equal to
E, so many also are there in
AB,
CD equal to
E,
F;