GEOMETRY GLOSSARY
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Title  Description  

Cardioid  A heartshaped curve formed by rotating a circle and graphing the movement of that point as the "outside" circle traces around the inside circle.  
Cartesian Coordinates  The familiar xy coordinate plane is called the plane of Cartesian Coordinates; it is named for Rene Descartes. 

Cartesian Plane  The Cartesian Plane contains the familiar xaxis and yaxis in which we plot ordered pairs. It is the familiar Rectangular Coordinate system. 

Center of Mass  The Center of Mass of an object is the point at which forces acting on the object may be considered to be balanced or concentrated. In a triangle it is at the centroid, the point of concurrence where the medians of the triangle meet. 

Center of Rotation  A point around which the rest of a body or object rotates is termed the Center of Rotation.  
Center of Rotation 2  The point around which an object revolves or rotates is called the Center of Rotation.  
Central Angle  A Central Angle is formed at the center of a circle. Think of the angle formed by cutting a slice of pie or cake from the center of a round baked good. 

Centroid  The Center of Mass of a triangle (made from some flat material) is its Centroid. It is the point at which the medians of the triangles intersect, also called the point of concurrence. 

Chord  A line (line segment) across a circle that does not pass through the center of the circle is termed a Chord.  
Circular Cone  A Circular Cone need not have its apex directly above the center of its base.  
Circular Cylinder  A Circular Cylinder does not have to have sides perpendicular to its base; its side may be oblique.  
Circumcenter  The center of a circumscribed circle is called its Circumcenter. All regular polygons have a circumcenter, but most polygons do not. All triangles have a circumcenter. 

Circumcircle  Also called the Circumscribed Circle, the Circumcircle encompasses a polygon and all vertices of the polygon are on the circle.  
Circumference  The distance around a circle is its Circumference. It is the product of pi times the diameter, or twice the product of pi and the radius of the circle. 

Circumscribed Circle  A circle around a polygon that contains all the vertices of that polygon is termed a Circumscribed Circle, also called a Circumcircle.  
Clockwise  Rotation in the same direction as the hands of a traditional clock.  
Collinear  Lined up perfectly; exactly aligned. In the same line are collinear points. 

Complement of an Angle  Complementary Angles sum to 90 degrees or pi/2 radians. So the complement of an angle with measure x is (90  x) degrees or (pi/2  x) radians. 

Complementary Angles  Complementary Angles sum to 90 degrees or pi/2 radians.  
Concave  Bending inward or with an indentation. The opposite of convex, Concave applies to physical objects such as lenses or mirrors, as well as to polygons or solids. 

Concave Polygon  A Concave Polygon has an "indentation." In moving around the perimeter of the polygon, at least one interior angle will be greater than 180 degrees.  
Concenric Circles  Circles having the same centers but different radii are termed Concentric Circles.  
Concentric  Literally having the same center point; centered at the same point.  
Conclusion  When mathematical conclusions are valid the laws of math and science have been adhered to, and a logical approach has been taken. Sometimes conclusions are invalid because scientific or mathematic rigor has not been adhered to. Reason and judgment are often important to reaching sound or valid conclusions. 

Concurrent  At the same point. Concurrent geometric entities occupy the same place, the same space. 

Cone  A Cone is a geometric shape where a simple closed curve is connected to an apex (a point) with smooth lateral sides.  
Congruence Test  There are various tests for congruence, which is the state of having identical size and shape.  
Conic Section  Any of the various geometric entities that are formed by slicing a cone (or double cone) are termed Conic Sections. The list includes: circles, ellipses, parabolas, and hyperbolas. 

Consecutive Interior Angles  When two parallel lines are cut by a transversal, the two angles formed on one side of the transversal between the parallel lines are termed Consecutive Interior Angles; they are supplementary.  
Contraction  Contraction is the process by which some object or entity is shrunk or diminished in size or extent. It may be diminished in one dimension, or reduced proportionally if it is a two or threedimensional object. A Contraction can also be the result of such a process. 

Contrapositive  Given a conditional statement, its Contrapositive is logically equivalent and is obtained by negating the original hypothesis and conclusion as well as reversing their order.  
Converse  Given a conditional statement, as "If A, then B," the Converse results from switching the order of the hypothesis and conclusion: "If B, then A." The Converse may or may not be true given a true original statement.  
Convex  When a geometric or physical entity has no indentations. Or, when a polygon has the property where no line segment across it leaves the interior of the polygon, the polygon is said to be Convex. 

Coordinate  A value associated with the location of a point is a Coordinate. In one dimension a Coordinate is a single value. In two dimensions, a point is defined by two Coordinates as an ordered pair. 

Coordinate Geometry  This branch of mathematics is a combination of algebra and geometry; it is analytic geometry.  
Coordinate Plane  Twodimensional entities are graphed or plotted in a plane, such as the rectangular plane or Cartesian Plane. Twodimensional polar coordinates are also plotted in a plane. It requires an ordered pair to specify a location in a plane. 

Coplanar  In the same plane; of the same plane. Most generally, points within the same plane are said to be Coplanar. 

Corollary  A Corollary is like a baby theorem.  
Corresponding Angles  Sometimes Corresponding Angles refer to the "same" angle in two similar (or congruent) polygons. Or, when parallel lines are cut by a transversal, Corresponding Angles are "on the same corner of the intersections." 

Coterminal  When one angle is in the same position as another, as adding or subtracting 360 degrees or 2 pi radians puts a rotating angle in the same position as the previous angle, we say the angles are Coterminal.  
Counterclockwise  For angles in standard position, we use a Counterclockwise rotation for positive measurement of the angle's rotation. This is the direction opposite the traditional movement of analog clock hands. 

CPCTC  In geometry class we use this shorthand for "Corresponding Parts of Congruent Triangles are Congruent."  
Cross Product  A product of vectors that generates another vector is often a Cross Product.  
Cube  A sixsided orthogonal box with square faces; a right square parallelepiped. The result of raising a real value to its third power. The process of multiplying a number times itself and times itself again. 

Curve  Beware that mathematicians consider straight lines to be Curves!  
Cycloid  The path that a point on the outside of a rolling wheel makes is termed a Cycloid.  
Cylinder  A Cylinder may or may not have circular bases. The lateral sides are connected with congruent, parallel bases that may be the shape of any closed curve. 
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