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If four quantities are in proportion, they are in proportion by composition; that is, the sum of the first two terms is to the second term as the sum of the last two terms is to the fourth term.
A Text-book of Geometry - Page 130
by George Albert Wentworth - 1888 - 386 pages

## New Plane and Solid Geometry

Webster Wells - Geometry - 1908 - 336 pages
...Proof. From (1), ad = be. (?) Then, £ = * (?) ac PROP. V. THEOREM 221. In any proportion, the terms are in proportion by COMPOSITION ; that is, the sum of the first two terms is to the first term as the sum of the last two terms is to the third term. Given the proportion a...

## Plane and Solid Geometry

Elmer Adelbert Lyman - Geometry - 1908 - 364 pages
...quantities are in proportion, they are in proportion by composition, ie the sum of the first two terms is to the second term as the sum of the last two terms is to the last term. f,. ac Given : To Prove : bd a+b _c+d bd Proof: f = ^. Then |+ ! = «+!. (Why?)...

## Wentworth's Plane Geometry

George Albert Wentworth, David Eugene Smith - Geometry, Plane - 1910 - 287 pages
...= d : c, by § 257. QED PROPOSITION IV. THEOREM 267. If four quantities are in proportion, they are in proportion by composition; that is, the sum of the first two terms is to the second term as the sum of the last two terms is to the fourth term. or Given a : b = c :...

## Plane Geometry

Clara Avis Hart, Daniel D. Feldman - Geometry, Modern - 1911 - 328 pages
...in the analysis of Prop. V. PROPOSITION V. THEOREM 398. If four numbers are in proportion, they are in proportion by composition; that is, the sum of the first two terms is to the first (or second) term as the sum of the last two terms is to the third (or fourth) term....

## New High School Algebra

Webster Wells, Walter Wilson Hart - Algebra - 1912 - 504 pages
...by oc. EXAMPLE. Since | = Д, then g should equal ^. Does it ? 311. In any proportion, the terms are in proportion by Composition ; that is, the sum of the first two terms is to the second as the sum of the last two terms is to the fourth. If £ =4 prove *¥ = *¥• bdbd...

## First Year Algebra

Webster Wells, Walter Wilson Hart - Algebra - 1912 - 344 pages
...ac. EXAMPLE. Since J = Д, then | should equal *?. Does it ? 221. In any proportion, the terms are in proportion by Composition ; that is, the sum of the first two terms is to the second as the sum of the last tico terms is to the fourth. If ? = £, prove a + b = c±d_...

## Plane Geometry

William Betz, Harrison Emmett Webb, Percey Franklyn Smith - Geometry, Plane - 1912 - 360 pages
...are in proportion, they are in proportion by addition ; that is, the sum of the first two terms is to the second term as the sum of the last two terms is to the fourth term. Proof. If ^ = v then ^ + 1=^ + 1. Why ? bdbd a + bc + d Then Similarly, bd a...

## Plane Geometry

William Betz, Harrison Emmett Webb - Geometry, Modern - 1912 - 368 pages
...are in proportion, they are in proportion by addition ; that is, the sum of the first two terms is to the second term as the sum of the last two terms is to the fourth term. Proof. If £ = -, then \ + \ = - + 1. Why ? Then Similarly, bdb ' d a + b _...