A Treatise on Elementary Geometry, with Appendices Containing a Collection of Exercises for Students and an Introduction to Modern Geometry

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J.B. Lippincott, 1879 - Geometry - 368 pages
 

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Page 346 - Three lines are in harmonical proportion, when the first is to the third, as the difference between the first and second, is to the difference between the second and third ; and the second is called a harmonic mean between the first and third. The expression 'harmonical proportion...
Page 214 - 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.
Page 128 - The area of a rectangle is equal to the product of its base and altitude.
Page 19 - The perpendicular is the shortest line that can be drawn from a point to a straight line.
Page 252 - The angle of two arcs of great circles is equal to the angle of their planes, and 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 and AB...
Page 313 - Find the locus of a point such that the sum of the squares of its distances from two fixed points shall be equivalent to the square of the distance between the fixed points.
Page 208 - If a pyramid is cut by a plane parallel to its base: 1st, the edges and the altitude are divided proportionally; 2d, the section is a polygon similar to the base. Let the pyramid...
Page 117 - The sum of the squares of the sides of any quadrilateral is equal to the sum of the squares of the diagonals plus four times the square of the line joining the middle points of the diagonals.
Page 261 - 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 217 - A truncated triangular prism is equivalent to the sum of three pyramids, whose common base is the base of the prism and whose vertices are the three vertices of the inclined section.

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