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Definitions and Examples ofGeometric Terms
Definition of a POINT
A point has no size and has only a location in space.
It is represented by a dot and named by capital letters.
A •
C •
B •
Definition of a LINE
A line is a straight arrangement of points.
It has length but no thickness and extends forever in both directions.
Lines are named using two points on the line.
Example
Name each line two different ways
Draw and label each line
Definition of a PLANE
A plane has length and width but no thickness.
It is a flat surface that extends forever.
Example
Definition of a LINE SEGMENT
A line segment consists of two points called endpoints and all the points between the endpoints.
Example
Name each line segment two different ways
Draw and label each line segment
Definition of a RAY
A ray is half a line.
Rays are named by its endpoint and a point on the ray.
Example
Name each ray two different ways
Draw and label each ray
Definition of an ANGLEAn angle is two rays that share a common endpoint where the two rays do not line on the same line.
VERTEX OF AN ANGLEThe common endpoint of two rays that make an angle.
SIDES OF AN ANGLEThe two rays that form an angle.
Example
Name each angle two different ways
Draw and label each angle
Measurements of an Angle
Degree meaure range from 0 to 360 degrees
Full rotation is a circle: 360 degrees
Half rotation is a line: 180 degrees
Quarter rotation is 90 degrees
Examples
How to measure an AnglePlace the center mark of the protractor on the vertex of the angle
Rotate the “zero-edge of the protractor to line up with one side of the angle
Read the measure of the angle on the protractor’s scale at the point where the other side crosses.
Exercise Set A
Marking angles and segmentswith same measures
Angles with the same measure are marked with an arc and the same number of slashes.
Segments with the same lengths are marked with the same number of slashes
Exercise Set D
Classification of Angles
Right angle: Angle with measure 90. Acute angle: Angle with measure between 0 and less than 90 Obtuse angle: Angle with measure greater than 90 and less than 180.
Examples
Definition of Midpoint of a Segment and an Angle Bisector
Midpoint of a segment: The point that divides the segment into two segments of equal measure.
Angle bisector:The ray that divides an angle into two angles of equal measure.
Examples
Definition of Collinear and Coplanar Points
Collinear points:Points all on one line.
Coplanar points:Points all on one plane.
Examples
Definition of Parallel and Perpendicular Lines
Parallel linesLines on the same plane that do not intersect.
Perpendicular linesTwo Lines that intersect to form right angles.
Examples
Definition of Pair of Complementary and Supplementary Angles
Pair of complementary anglesTwo angles that equal 90 degrees.
Pair of supplementary anglesTwo angles that equal 180 degrees
Examples:
Definition of PolygonsPolygons A closed geometric figure in a plane formed with at least three sides that are segments. The sides intersect only at their endpoints. No two adjacent sides are collinear.
Convex PolygonsNo segment connecting two vertices is outside the polygon
Concave PolygonsAt least one segment connecting two vertices is outside the polygon
Examples:
Classification of Polygons
Number of sides 3 Triangle4 Quadrilateral5 Pentagon6 Hexagon7 Heptagon8 Octagon9 Nonagon10 Decagon
Examples:
Naming Polygons; Diagonals of Polygons
Naming Polygons Use the letters in consecutive order.
Diagonals of PolygonsA segment that connects nonconsecutive vertices of a polygon.
Examples:
Special Polygons
Equilateral Polygons All sides are congruent (same measure).
Equiangular PolygonsAll angles are congruent.
Regular PolygonsAll sides and angles are congruent.
Examples:
Definition of Triangles
Right Triangle One right angle
Acute TriangleAll acute angles
Obtuse TriangleOne obtuse angle
Examples:
Definition of Triangles
Scalene Triangle No sides are congruent
Isosceles TriangleTwo sides are congruent
Equilateral TriangleAll sides are congruent
Examples:
Median and Altitude of a Triangle
Median of a Triangle A segment from the midpoint of one side of a triangle to the opposite vertex.
Altitude of a TriangleThe perpendicular segment from a vertex of a triangle to the line containing the opposite side.
Examples:
Definition of Special QuadrilateralsQuadrilateralA 4-sided polygon
RectangleA quadrilateral with four right angles.
SquareA quadrilateral with four right angles four congruent sides .
Examples:
Definition of Special Quadrilaterals
TrapezoidA quadrilateral with exactly one pair of parallel sides.
ParallelogramA quadrilateral with both pairs of opposite sides parallel.
RhombusA quadrilateral with four congruent sides.
Examples:
