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West ; add them together. 3. If both are North or South, but one East and the other West; subtract their sum from 180 degrees. 4. If both are North or South, and both East or West ; add together 90 degrees...
A System of Geometry and Trigonometry: With a Treatise on Surveying ... in ... - Page 52
by Abel Flint - 1830 - 284 pages

## A Course of Mathematics: Containing the Principles of Plane Trigonometry ...

Jeremiah Day - Geometry - 1839 - 370 pages
...any two contiguous sides make with each other, may be known by the following rules. 1. If one course is North and the other South, one East and the other West ; subtract the less from the greater. 2. If one is North and the other South, but both East or West ; add them together....

## A Course of Mathematics: Containing the Principles of Plane Trigonometry ...

Jeremiah Day - Geometry - 1851
...any two contiguous sides make with each other, may be known by the following rules. 1. If one course is North and the other South, one East and the other West ; subtract the less from the greater. 2. If one is North and the other South, but both East or West ; add them together....

## Elements of Plane Trigonometry, Surveying and Navigation

William Smyth - Navigation - 1855 - 223 pages
...drawing meridian lines though the corners. The angles may be found by the following rules. 1°. If the bearing of one of the sides is north and the other...other west, subtract the less course from the greater. 2°. If one is north and the other south, and both east or west, add both courses together. 3°. If...