Plane a.  Without elevations or depressions; even; level; flat; lying in, or constituting, a plane; as, a plane surface.
 Note: ☞ In science, this word (instead of plain) is almost exclusively used to designate a flat or level surface.
 Plane angle, the angle included between two straight lines in a plane.
 Plane chart, Plane curve. See under Chart and Curve.
 Plane figure, a figure all points of which lie in the same plane. If bounded by straight lines it is a rectilinear plane figure, if by curved lines it is a curvilinear plane figure.
 Plane geometry, that part of geometry which treats of the relations and properties of plane figures.
 Plane problem, a problem which can be solved geometrically by the aid of the right line and circle only.
 Plane sailing Naut., the method of computing a ship's place and course on the supposition that the earth's surface is a plane.
 Plane scale Naut., a scale for the use of navigators, on which are graduated chords, sines, tangents, secants, rhumbs, geographical miles, etc.
 Plane surveying, surveying in which the curvature of the earth is disregarded; ordinary field and topographical surveying of tracts of moderate extent.
 Plane table, an instrument used for plotting the lines of a survey on paper in the field.
 Plane trigonometry, the branch of trigonometry in which its principles are applied to plane triangles.


 Trig·o·nom·e·try n.; pl. -tries
 1. That branch of mathematics which treats of the relations of the sides and angles of triangles, which the methods of deducing from certain given parts other required parts, and also of the general relations which exist between the trigonometrical functions of arcs or angles.
 2. A treatise in this science.
 Analytical trigonometry, that branch of trigonometry which treats of the relations and properties of the trigonometrical functions.
 Plane trigonometry, and Spherical trigonometry, those branches of trigonometry in which its principles are applied to plane triangles and spherical triangles respectively.

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