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To express that the ratio of A to B is equal to the ratio of C to D, we write the quantities thus : A : B : : C : D; and read, A is to B as C to D.
Manual of Geometry and Conic Sections: With Applications to Trigonometry and ... - Page 70
by William Guy Peck - 1876 - 366 pages

## New Elementary Algebra Embracing the First Principles of the Science

Charles Davies - Algebra - 1891 - 312 pages
...D, having such values that B=D A C' then A is said to have the same ratio to B that C has to D, or the ratio of A to B is equal to the ratio of C to D. "When four quantities have this relation to each other, compared together two and two, they are said...

## The Electrical Review, Volume 4

Electrical engineering - 1876 - 352 pages
...where the wires diverge and meet again. When the resistances of A, B, C, and D are so related that the ratio of A to B is equal to the ratio of C to D, then the points E and F are at the same level or the same potential with regard to electricity, and...

## Transactions of the Cambridge Philosophical Society

Cambridge Philosophical Society - Philosophy - 1898 - 366 pages
...the measure of the ratio of A to B is the same as the measure of the ratio of C to D, and therefore the ratio of A to B is equal to the ratio of C to D. Hence any of the preceding propositions in which it has been proved that the scale of A, B is the same...