1. Definitions and Examples of Geometric Terms

2. Definition of a POINT A • C • B •
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 •

3. Definition of a LINE Example Name each line two different ways
Draw and label each 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.

4. Definition of a PLANE Example
A plane has length and width but no thickness.
It is a flat surface that extends forever.

5. Definition of a LINE SEGMENT
Example
Name each line segment two different ways
Draw and label each line segment
A line segment consists of two points called endpoints and all the points between the endpoints.

6. Definition of a RAY Example Name each ray two different ways
Draw and label each ray
A ray is half a line.
Rays are named by its endpoint and a point on the ray.

7. Definition of an ANGLE Example Name each angle two different ways
Draw and label each angle
An angle is two rays that share a common endpoint where the two rays do not line on the same line.
VERTEX OF AN ANGLE
The common endpoint of two rays that make an angle.
SIDES OF AN ANGLE
The two rays that form an angle.

8. Measurements of an Angle
Examples
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

9. How to measure an Angle Exercise Set A
Place 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.

10. Marking angles and segments with same measures
Exercise Set D
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

11. 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

12. 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

13. Definition of Collinear and Coplanar Points
Collinear points:
Points all on one line.
Coplanar points:
Points all on one plane.
Examples

14. Definition of Parallel and Perpendicular Lines
Parallel lines
Lines on the same plane that do not intersect.
Perpendicular lines
Two Lines that intersect to form right angles.
Examples

15. Definition of Pair of Complementary and Supplementary Angles
Pair of complementary angles
Two angles that equal 90 degrees.
Pair of supplementary angles
Two angles that equal 180 degrees
Examples:

16. Definition of Polygons
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 Polygons
No segment connecting two vertices is outside the polygon
Concave Polygons
At least one segment connecting two vertices is outside the polygon
Examples:

17. Classification of Polygons
Number of sides
3 Triangle
4 Quadrilateral
5 Pentagon
6 Hexagon
7 Heptagon
8 Octagon
9 Nonagon
10 Decagon
Examples:

18. Naming Polygons; Diagonals of Polygons
Use the letters in consecutive order.
Diagonals of Polygons
A segment that connects nonconsecutive vertices of a polygon.
Examples:

19. Special Polygons Examples: Equilateral Polygons
All sides are congruent (same measure).
Equiangular Polygons
All angles are congruent.
Regular Polygons
All sides and angles are congruent.
Examples:

20. Definition of Triangles
Right Triangle
One right angle
Acute Triangle
All acute angles
Obtuse Triangle
One obtuse angle
Examples:

21. Definition of Triangles
Scalene Triangle
No sides are congruent
Isosceles Triangle
Two sides are congruent
Equilateral Triangle
All sides are congruent
Examples:

22. 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 Triangle
The perpendicular segment from a vertex of a triangle to the line containing the opposite side.
Examples:

23. Definition of Special Quadrilaterals
A 4-sided polygon
Rectangle
A quadrilateral with four right angles.
Square
A quadrilateral with four right angles four congruent sides .
Examples:

24. Definition of Special Quadrilaterals
Trapezoid
A quadrilateral with exactly one pair of parallel sides.
Parallelogram
A quadrilateral with both pairs of opposite sides parallel.
Rhombus
A quadrilateral with four congruent sides.
Examples: