# A Text-book of Geometry

Ginn, 1892 - Geometry - 437 pages

### Contents

 STRAIGHT LINES 2 PLANE ANGLES 7 SYMMETRY 13 THE CIRCLE 75 PROPORTIONAL LINES AND SIMILAR POLYGONS 131 AREAS OF POLYGONS 180 17 199
 REGULAR POLYGONS AND CIRCLES 209 PROBLEMS OF CONSTRUCTION 222 LINES AND PLANES IN SPACE 243 POLYHEDRONS CYLINDERS AND CONES 278 THE SPHERE 339 209 406

### Popular passages

Page 88 - Any two sides of a triangle are together greater than the third side.
Page 340 - A spherical angle is measured by the arc of a great circle described from its vertex as a pole and included between its sides (produced if necessary). Let AB, AC be arcs of great circles intersecting at A; AB...
Page 61 - The exterior angles of a polygon, made by producing each of its sides in succession, are together equal to four right angles.
Page 323 - The volume of a frustum of a cone is equivalent to the sum of the volumes of three cones whose common altitude is the altitude of the frustum and whose bases are the lower base, the upper base, and a mean proportional between the bases of the frustum.
Page 179 - Two triangles having 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.
Page 56 - The straight line joining the middle points of two sides of a triangle is parallel to the third side and equal to half of it 46 INTERCEPTS BY PARALLEL LINES.
Page 140 - If two triangles have an angle of the one equal to an angle of the other, and the including sides proportional, they are similar. In the triangles ABC and A'B'C', let ZA = Z A', and let AB : A'B' = AC : A'C'. To prove that the A ABC and A'B'C' are similar. In this case we prove the A similar by proving them mutually equiangular. Proof. Place the A A'B'C...
Page 126 - 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.
Page 346 - The sum of the angles of a spherical triangle is greater than two and less than six right angles ; that is, greater than 180° and less than 540°. (gr). If A'B'C' is the polar triangle of ABC...
Page 342 - A spherical polygon is a portion of the surface of a sphere bounded by three or more arcs of great circles. The bounding arcs are the sides of the polygon ; the...