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point: has no size, is infinitely small, and has a location. line: an infinite arrangement of points plane: a two-dimensional surface that extends infinitely in all directions space: the unbounded three-dimensional expanse in which all matter exists collinear points: points that lie on the same line coplanar points: points that lie on the same plane line segment: Two end points with all the points between them ray: contains a point, and all the points on one side of it angle: two rays leaving from the same point vertex: the common endpoint of an angle sides (of an angle): the two rays of an angle supplementary angles: two angles whose angle measurements, when added, are 180 degrees right angle: an angle whose measurement is 90 degrees acute angle: and angle that has less than 90 degrees obtuse angle: an angle that measures more than 90 degrees midpoint (of a segment): the point that divides a segment into two equal halves angle bisector: a ray that divides an angle exactly in half on a plane parallel lines: lines with the same slope that never intersect on a plane perpendicular lines: two lines that intersect to form a right angle pair of complementary angles: two angles that add up to 90 degrees pair of vertical angles: either of the pair of equal angles formed on opposite sides of the point at which two lines intersect. The sides of either of the pair of vertical angles are the extensions of those of the other angle. pair of linear angles: two angles that form a line right triangle: a triangle with a 90 degree angle in it acute triangle: a triangle with all angles less than 90 degrees obtuse triangle: a triangle with one angle more than 90 degrees scalene triangle: a triangle which none of its sides are congruent isosceles triangle: a triangle with at least two congruent sides median of a triangle: a line segment extending from the midpoint of a side to a nonadjacent vertex (three possible medians in every triangle) altitude of a triangle: a line segment starting at a vertex and extending perpendicularly to the opposite side (or extension of the opposite side) trapezoid: a quadrilateral in which exactly one pair of sides are parallel kite: a quadrilateral with two pairs of congruent sides and no parallel sides parallelogram: a quadrilateral with two pairs of parallel sides rhombus: a parallelogram with four equal sides rectangle: a parallelogram with 4 90 degree angles square: a rectangle with equal sides polygon: a closed geometric figure in a plane, formed by connecting line segments, endpoint to endpoint with each segment intersecting two others side (of a polygon): a line segment in a polygon vertex (of a polygon): An endpoint where sides meet in a polygon convex polygon: a polygon in which no segment connecting two vertices is outside the polygon concave polygon: a polygon in which at least one segment connecting two vertices is outside the polygon consecutive vertices: two vertices connected by a side consecutive sides: two sides sharing a common vertex consecutive angles: two angles sharing a common side congruent polygons: two or more polygons that are exactly the same size and shape perimeter: the sum of the lengths of a polygon's sides diagonal of a polygon: a line segment connecting two non adjacent vertices of a polygon equilateral polygon: polygon with all equal sides equiangular polygon: polygon with all equal angles regular polygon: polygon with all equal angles and sides sketch: free hand diagram not necessarily accurate, but needs markings. draw: more accurate diagram by using measuring tools (protractor and/or ruler) construction: accurate representation by using compass and straight edge centroid: the point of concurrency of three medians in a triangle. circumcenter: the point of concurrency of three perpendicular bisectors in a triangle orthocenter: point of concurrency of the three altitudes in a triangle circumscribed: to draw one geometrical figure around another so that they touch at every vertex of the enclosed figure or at every side of the enclosing figure without cutting across each other incenter: the point of concurrency of the three angle bisectors in a triangle point of concurrency: point of intersection inscribed: to draw a geometric figure within another so that all of the second figure lies within the first and touches it at as many points as possible transversal: a line that intersects two or more coplanar points corresponding angle: the angles formed on the same side of two lines and a third line ( transversal ) that intersects them, each of the four angles at each intersection corresponding to the four angles at the other alternate interior angles: two angles on opposite sides of transversal, inside both lines alternate exterior angles: two angles on opposite sides of transversal exterior angle: an angle on the outside of a polygon, formed between a side and an extension of an adjacent side circle: a curved line surrounding a center point, every point of the line being an equal distance from the center point secant: a straight line that intersects with a curve in two or more places tangent: a line, curve, or surface that touches another curve or surface but does not cross or intersect it diameter: a straight line running from one side of a circle through the center to the other side radius: a straight line extending from the center of a circle to its edge |