Geometry Vocabularyacute angle-an anglemeasuring less than90 degreesangle-the turn or bendbetween twointersecting lines, linesegments, rays, orplanesangle bisector-anangle bisector is a raythat cuts an angleexactly in half,making two equalangles45 45 circle-the set of allpoints in a plane thatare a given distancefrom a given pointcircumference-thedistance around theedge of a circle.closed figure-theboundary of a simpletwo-dimensionalregion, includingshapes with straightand curved sidescone- threedimensional figurewith a curved surface,a circular base andone apex (point)attribute- acharacteristic of anobject, such as color,shape, or sizebase-a face or surface(3-D object) or a side(2-D objects)considered as thebottom part, orfoundation of ageometric figure; usedfor the purpose ofmeasurementbasecongruent- geometricfigures having thesame size and shape;all correspondingparts of congruentfigures have the samemeasurecoordinate plane-thegrid system in whichthe x-axis and y-axisprovide referencepointsdiameter-the distanceacross the widest partof a circle; twice theradius; also defined asa chord that passesthrough the center ofa circlecube-a threedimensional objectwith 6 square facesdilation- shrinking orstretching the figurecylinder- threedimensional figurewith a curved surfaceand two circular basesedge- a line segmentat the intersection oftwo faces of apolyhedrondegree-a unit ofmeasure of angles;there are 360 degreesin a circlediagonal- for apolygon in the plane,any line segmentjoining non-adjacentvertices.equiangulartriangle- a trianglewhich all angles arecongruentequilateral trianglea triangle which allthe sides arecongruent.

face- a polygonalregion of a threedimensional figureheptagon- a polygonwith seven sideshexagon- A polygonwith six sidesline-one of the threeundefined figures ingeometry, a line hasno thickness, isperfectly straight, andgoes on forever inboth directions; twopoints determine aunique lineline of symmetry-aline over which afigure can bereflected, resulting ina figure that looksexactly like theoriginalintersecting lineslines that meet orcrossisosceles triangle-atriangle having twosides, called the legs,of equal lengthoctagon- a polygonwith eight sidesone-dimensional- afigure that has lengthbut no width orheight.parallel lines- Linesthat lie in the sameplane and never meet.Also, planes lying inspace that never meet.parallelogram-aquadrilateral withboth pairs of oppositesides parallel.line segment-a finiteportion of a line, oftendenoted by its endpointspentagon- a polygonwith five sidesnet- a blueprint, orpattern, for a threedimensional model.kite-a quadrilateralwith two pairs ofadjacent sides withequal lengths.obtuse angle-an anglemeasuring between 90and 180 degreesperpendicular lineslines in the sameplane which intersectto form a right angle.plane-one of the threeundefined figures ingeometry, a plane is aflat expanse, like asheet of paper, thatgoes on foreverplane figure-any twodimensional figurepoint-one of the threeundefined figures ingeometry, a point is alocation with nolength, width, andheight.polygon-a twodimensional closedfigure made up ofstraight line segments.polyhedron-a threedimensional closedfigure made up offaces that are allpolygonsprism- a threedimensional figurewith parallelogramfaces and two parallel,congruent bases

pyramid- a geometricsolid with a base thatis a polygon and allother faces aretriangles with acommon vertexrectangular prism- athree-dimensionalfigure withparallelogram facesand two parallel,congruent rectangularbases. quadrilateral-apolygon with foursidesrectangle-aquadrilateral in whichall the angles have thesame measure (90degrees)similar-two or morefigures having thesame shape but notnecessarily the samesizeright angle- an anglemeasuring 90 degreesrectangularpyramid- a geometricsolid with a base thatis a rectangle and allother faces aretriangles with acommon vertexradius-the distancefrom the center of acircle to any point onits edge; half adiameterray-a portion of a lineextending in onedirection from a pointrhombus- aquadrilateral in whichall sides have thesame lengthslide- see translationsolid figure- a closed,three dimensionalfigurerotation (turn)- atransformationobtained by rotating afigure around a fixedpoint (i.e., turning afigure about a point).reflection (flip)-atransformation whichproduces the mirrorimage of a figure (i.e.,flipping a figureacross a line) scalene- a polygon isscalene if its sides areall different lengthsregular polygon- apolygon in which allangle and all sides arecongruent; examplesequilateral triangle,square, regularoctagonsphere-the set of allpoints in threedimensional spacethat are located at agiven distance fromthe centerside- a line segment atthe boundary of apolygonsquare- a regularquadrilateral (all sidesand angles arecongruent)symmetry- a figurehas symmetry if thereexists some line orpoint through whichall points of the figurecan be reflected togenerate another pointon the figure

tessellation- coveringof the plane,sometimes referred toas a tiling, referring tothe way that tilescover a floortriangular prism- athree-dimensionalfigure withparallelogram facesand two parallel,congruent triangularbases three-dimensionalan object that haslength, width, andheighttransformation- arule for moving everypoint in a plane figureto a new locationtranslation (slide)- atransformation thatslides a figure a givendistance in a givendirectiontrapezoid (inclusive)- a quadrilateral withat least one set ofparallel sides.triangle- a polygonwith three sidestriangular pyramid a geometric solid witha base that is atriangle and all otherfaces are triangleswith a common vertex turn- see rotationtwo-dimensional- afigure that has lengthand width but notheight (i.e., a planefigure such as arectangle or circle)vertex (vertices)- thepoints where two linesegments cometogether (corner