Geometry Vocabulary.
Geometry of Plane figures.
Mr. Piotrowski 2012
Point: is an exact location in space.
Space: is the collection of all points.
Line: is a straight, continuous, and unending collection of points.
Line Segment: is a part of a line with two endpoints
Ray: is a straight, continuous, and unending set of points that has one endpoint.
Plane: A flat surface made up of a continuous and unending collection of points
Angle: a figure formed by two rays with a common endpoint. The part of a plane between the
two rays is called interior of the angle.
Vertex: a point common to two sides of an angle or polygon
Polygon: a simple closed plane figure made up of three or more line segments (has straight sides
that form angles.); a polygon is a simple closed plane figure formed by three or more line
segments meeting only at their endpoints.
Regular Polygon: is a polygon with all sides congruent and all angles congruent.
Polygons include:
Triangle
3 sides
Quadrilateral
4
Pentagon
5
Hexagon
6
Heptagon
7
Octagon
8
Nonagon
9
Decagon
10
Undecagon
11
Dodecagon
12 sides
Vertical angles: When two straight lines intersect, two pairs of congruent vertical angles are
formed.
Adjacent angels share a common side and a common vertex and their interiors do not overlap.
Complementary angles: The sum of the measures of two complementary angles is 90 degrees.
Supplementary angles: The sum of the measures of two supplementary angles is 180 degrees.
Right angle: The measure of a right angle is 90 degrees.
Acute angle: The measure of an acute angle is less than 90 degrees.
Obtuse angle: The measure of an obtuse angle is greater than 90 degrees and less than 180
degrees.
Center (of a circle) is the point that is the same distance from all points on the circle.
Radius: a radius is any segment tht has n=one endpoint at the center of the circle and the other
endpoint on the circle. The same word also describes the length of that segment. The plural of
radius is radii.
Chord: a chord is any segment with both endpoints on the circle.
Diameter: a line segment that connects two points on a circle and passes though the
circle’s center.
Central Angle: a central angle is any angle with its vertex at the center of the circle and sides
that intersect the circle.
Congruent: Shapes that are congruent are the same size and same shape
Similar: Shapes that are similar have the same shape but do not have to be the same size. (The
side lengths should be in the same proportion like an equivalent fraction.)
Diagonal: A line segment that connects opposite vertices of a closed figure and is not a side.
Geometry Vocabulary.
m∟n
Geometry of Plane figures.
Mr. Piotrowski 2012
means “the angle measurement of angle n”
Equilateral Triangle: all sides congruent length
Isosceles Triangle: at least two sides congruent length
Scalene Triangle: no sides congruent length
Right Triangle: One 90 degree angle
Acute Triangle: Three acute angles
Obtuse Triangle: One obtuse angle
Quadrilateral Properties:
Parallelogram: A quadrilateral with opposite sides parallel. The opposite sides and
opposite angles are also congruent.
Rectangle: A quadrilateral with four fight angles. A rectangle is also a parallelogram.
Square: A rectangle with all sides congruent.
Rhombus: A quadrilateral with all sides congruent. A rhombus is also a parallelogram.
Trapezoid: A quadrilateral with one pair of parallel sides.
Kite: A quadrilateral with two distinct pairs (pairs cannot have a side in common) of
equal adjacent sides. Note that a square and a rhombus are specific kites.
Trapezoid: Notice segment EF is parallel to segment HG.
ABCD is not an isosceles trapezoid because AD and BC are not congruent. Because EH and FG are
congruent, trapezoid EFGH is an isosceles trapezoid.