TRIGONOMETRY GLOSSARY
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Title  Description  

Radian  A Radian is an angle (measure) that subtends an arc length (on a circle) equal to the radius of the circle. Radians are just as good as degrees for measuring angles, and sometimes better. 

Radian Measure  Radian Measure is just as good as degree measure for angles, and sometimes better. Pi radians are equivalent to 180 degrees. 

Radical  A root symbol or the root itself is sometimes termed a Radical. 

Radius  Onehalf the diameter of a circle is the Radius. It is the distance from the center of a circle to any point on the circle. 

Ratio  Sometimes Ratio is meant to state a constant proportion. More generally, the Ratio of two real values is the quotient of one number divided by the other. 

Ray  A set of collinear points, a Ray has an endpoint and proceeds infinitely far in a single direction. 

RectangularPolar Conversion  A simple algorithm to change (x, y) into (r, theta). 

Reference Angle  In standard position, any angle in quadrants II, III, or IV has a Reference Angle equal to the acute angle made with the xaxis. 

Regular Polygon  A Regular Polygon is both equilateral (all sides congruent) and equiangular (all angles congruent). 

Regular Right Prism  A Prism with bases of Regular polygons and lateral faces perpendicular to those bases. 

Regular Right Pyramid  A Pyramid with a Regular polygon for a base and an apex directly above the center of the base. 

Revolutions Per Minute  Abbreviated "rpm" it conveys the number of complete circular rotations that occur every 60 seconds at some constant rate of revolution. 

Rho  Lowercase Rho, the 17th letter of the Greek alphabet, is often used for density (mass per unit volume) in physics. 

Right Angle  An angle of 90 degrees or pi/2 radians. Perpendicular lines meet at Right Angles. 

Right Circular Cone  A cone with a circular base and an apex directly above the center of the base. 

Right Circular Cylinder  A circular cylinder with sides orthogonal to parallel bases.  
Right Cone  Any Cone, circular or otherwise, with its apex directly above the center of the base. 

Right Cylinder  Any Cylinder, circular or otherwise, with lateral sides orthogonal to the bases. 

Right Prism  A Prism with lateral sides orthogonal to the bases. 

Right Pyramid  A Pyramid with its apex directly above the center of the base. 

Right Regular Prism  A Prism with bases of Regular polygons and lateral faces perpendicular to the bases. 

Right Regular Pyramid  A Pyramid with a Regular polygon for a base and an apex directly above the center of the base. 

Right Square Parallelepiped  Cube.  
Right Square Prism  A cube, or a shoebox if the ends of the shoebox are square. 

Right Triangle  A triangle with a right angle. 

Rotation  Movement in a circulation or circular fashion, often around a point or an axis, is termed Rotation. 
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