 | Claude Irwin Palmer, Daniel Pomeroy Taylor, Eva Crane Farnum - Geometry, Modern - 1924 - 360 pages
...second as the difference of the last two terms is to the fourth. (5) Addition and subtraction; that is, the sum of the first two terms is to their difference...as the sum of the last two is to their difference. Proofs _. ac Given - = -. bd Then ad = bc. § 350 (1) Alternation: - = -• §354 cd (2) Inversion:... | |
 | Edward Ira Edgerton, Perry Amherst Carpenter - Algebra - 1925 - 398 pages
...If four quantities are in proportion, they are in proportion by addition and subtraction, that is, the sum of the first two terms is to their difference as the sum of the last two terms is to their difference. Ex., if a : b = c : d, then (a + b) : (a — b) = (c + d):(c- d). Hint:... | |
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In any proportion the terms are in proportion by Composition and Division ; that is, the sum of the first two terms is to their difference, as the sum of the last two terms is to their difference. 
