PROTRACTOR—Instrument used for measuringand laying off angles.PYRAMID—A figure having a plane polygon forits base and triangles meeting at a common vertexfor its sides.PYTHAGOREAN THEOREM—A law ofmathematics that states that the square of thehypotenuse of a right triangle equals the sum ofthe squares of the other two sides.QUADRILATERAL—A polygon bounded byfour sides.QUALITATIVE CHART OR GRAPH—Anychart that emphasizes the relationships of facts.QUANTITATIVE CHART OR GRAPH—Achart or graph that emphasizes numerical values.RADIAN—A system for measuring angles where2nradians equals 360°; 1 radian = 57.3°.RADICAL—A symbol placed on a mathematicalquantity to indicate the root of the quantity; forexample.RADIUS-A straight line from the center of acircle or sphere to its circumference or surface.RATIO-A comparison of two like quantities; forexample, 2/3, 2:3.RATIONAL NUMBER—A number that can beexpressed as the quotient or ratio of two wholenumbers: Fractions 2/7, Integers 3/1 = 3. Aradical is a rational number if the radical isremovable; for example, ~ = 2, @ = 3.REAL NUMBERS—All positive and negativenumbers.RECIPROCAL—The reciprocal ofequals 1 divided by the number.RECTANGLE—A parallelogramadjacent sides join at right angles.a numberin whichRECTANGULAR PRISM—A solid figure whosebase is a rectangle.REFERENCE PLANE—The normal plane fromwhich all information is referenced.REGULAR POLYGON—An equilateral polygon.RESIDUAL SOIL—Any soil that results fromweathering in place and that is not moved fromits place of origin.RETICLE—A system of wires, hairs, threads,etched lines, or the like, placed normal to the axisof a telescope at its principal focus by means ofwhich the telescope is sighted on a star, or target,or by means of which appropriate readings are madeon some scale, such as a leveling or stadia rod.REVERSE CURVE—See OGEE CURVE.REVISION BLOCK—Block drawn in the upperright corner of construction drawings; containschronological list of all changes or revisions tothe drawing.REVOLUTION—Object is projected on one ormore of the planes of projection but rather thanbeing in the normal position, it is revolved on anaxis perpendicular to one of the regular planes;used when it can show the features of an objectmore clearly than a normal orthographic projection.REVOLVED SECTION—A sectional view usedto show the internal structure of an item withinthe normal orthographic view.RHOMBOID—A nonequilateral parallelogram inwhich adjacent sides join at oblique angles.RHOMBUS—An equilateral parallelogram inwhich adjacent sides join at oblique (other thanright) angles.RIGHT ANGLE—An angle of 90°.ROOT—The number of times a quantity is foundas an equal factor within another quantity; forexample.$%=4th root of 16 = 2AI-12
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