## First Part of an Elementary Treatise on Spherical Trigonometry |

### From inside the book

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**Secondly**. From triangle A'B'C ' we have by ( 5 ) ( 437 ) and ( 428 ) , and the fact that the angle B'A'C ' is equal to the inclination of the two planes BOC and BOA , ( 438 ) cos . B'A'C ' cos . A = A'C A'B and , from triangles A'OC ... Page 8

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**Secondly**. If co . A were made the middle part ; then , by ( 473 ) , co . h and b would be adjacent parts , and co . B and a opposite parts ; and , by ( 474 ) and ( 475 ) , we should have ( 480 ) ( 481 ) sin . ( co . A ) = sin . ( co ... Page 13

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**Secondly**. When either side is equal to 90 ° , it fol- lows , from ( 523 ) and ( 526 ) , that h = 90 ° . This result , substituted in equation ( 448 ) , sin . a = sin . h sin . A , ( 530 ) ( 531 ) produces , by ( 158 ) , ( 532 ) 2 CH ... Page 15

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**Secondly**. As the preceding equation expresses , that when the right angle is the greatest angle of the triangle it is less than the sum of the other two angles ; ( 546 ) we have only to show farther , that , when either of the other ... Page 17

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**Secondly**. To find the opposite leg a . The three parts are co . A , co . h , and a ; of which , by ( 556 ) , a is the middle part , and co . h and co . A are the opposite parts . Hence , by ( 475 ) , { or sin . a cos . ( co . h ) cos ...### Other editions - View all

First Part of an Elementary Treatise on Spherical Trigonometry (Classic Reprint) Benjamin Peirce No preview available - 2017 |

First Part of an Elementary Treatise on Spherical Trigonometry Benjamin Peirce No preview available - 2016 |

### Common terms and phrases

A'BC ABC+ the surface AC the perpendicular adjacent angles angles are given angles respectively equal AP and PC ar.co B'OC Corollary cosec cosine of half cotan Demonstration differs from 90 equal to 90 fall on AC given angle given leg given sides given value greater than 90 h tang half the sum Hence hypothenuse included angle Lemma less from 90 less than 90 Let ABC fig let fall logarithm lunary surface means of 496 middle negative obtuse opposite angle opposite side perpendicular BP perpendicular to OA planes BOC Problem quotient right angle right triangle fig right triangle PBC Scholium second member Secondly side BC sides and angles sides equal Solution of Spherical solve a spherical solve the triangle spherical right triangle spherical triangle ABC SPHERICAL TRIGONOMETRY substituted supplements surface ABC tangent of half Thirdly tive trian triangle ABC figs

### Popular passages

Page 69 - The areas of two triangles which have an angle of the one equal to an angle of the other are to each other as the products of the sides including the equal angles. D c A' D' Hyp. In triangles ABC and A'B'C', ZA = ZA'. To prove AABC = ABxAC. A A'B'C' A'B'xA'C' Proof. Draw the altitudes BD and B'D'.

Page 1 - A spherical triangle is a portion of the surface of a sphere, bounded by three arcs of great circles.

Page 69 - THEOREM. The surface of a spherical triangle is measured by the excess of the sum of its three angles above two right angles, multiplied by the tri-rectangular triangle.

Page 8 - I. The sine of the middle part is equal to the product of the tangents of the adjacent parts.

Page 8 - II. The sine of the middle part is equal to the product of the cosines of the opposite parts.

Page 30 - Any angle is greater than the difference between 180° and the sum of the other two angles.

Page 51 - The cosine of half the sum of two sides of a spherical triangle is to the cosine of half their difference as the cotangent of half the included angle is to the tangent of half the sum of the other two angles.

Page 51 - The cosine of half the sum of two angles of a spherical triangle is to the cosine of half their difference as the tangent of half the included side is to the tangent of half the sum of the other two sides.

Page 71 - ... and the sum of the angles in all the triangles is evidently the same as that of all the angles of the polygon ; hence, the surface of the polygon is equal to the sum of all its angles, diminished by twice as many right angles as it has sides less two, into the tri-rectangular triangle.