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A rhombohedron has two opposite apices at which all face angles are equal; a prolate rhombohedron has this common angle acute, and an oblate rhombohedron has an obtuse angle at these vertices. A cube is a special case of a rhombohedron with all sides square.
An acute triangle (or acute-angled triangle) is a triangle with three acute angles (less than 90°). An obtuse triangle (or obtuse-angled triangle) is a triangle with one obtuse angle (greater than 90°) and two acute angles. Since a triangle's angles must sum to 180° in Euclidean geometry, no Euclidean triangle can have more than one obtuse ...
The faces are isosceles triangles with one obtuse and two acute angles. The obtuse angle equals arccos(– 7 / 18 ) ≈ 112.885 380 476 16 ° and the acute ones equal arccos( 5 / 6 ) ≈ 33.557 309 761 92 °.
The obtuse or oblate or flat form has three obtuse angle corners of the rhombic faces meeting at the two polar axis vertices. More strongly than having all faces congruent, the trigonal trapezohedra are isohedral figures , meaning that they have symmetries that take any face to any other face.
Obtuse may refer to: Obtuse angle, an angle of between 90 and 180 degrees; Obtuse triangle, a triangle with an internal angle of between 90 and 180 degrees; Obtuse leaf shape; Obtuse tepal shape; Obtuse barracuda, a ray-finned fish; Obtuse, a neighborhood in Brookfield, Connecticut
An angle equal to 1 / 4 turn (90° or π / 2 radians) is called a right angle. Two lines that form a right angle are said to be normal, orthogonal, or perpendicular. [12] An angle larger than a right angle and smaller than a straight angle (between 90° and 180°) is called an obtuse angle [11] ("obtuse" meaning "blunt").
The parameters most commonly appearing in triangle inequalities are: the side lengths a, b, and c;; the semiperimeter s = (a + b + c) / 2 (half the perimeter p);; the angle measures A, B, and C of the angles of the vertices opposite the respective sides a, b, and c (with the vertices denoted with the same symbols as their angle measures);
The straight lines which form right angles are called perpendicular. [8] Euclid uses right angles in definitions 11 and 12 to define acute angles (those smaller than a right angle) and obtuse angles (those greater than a right angle). [9] Two angles are called complementary if their sum is a right angle. [10]