1. Geometry Basic Terms
Unit 1 Vocabulary

2. Angle
Two rays with the same vertex that are not opposite.

3. Adjacent Angles
Two coplanar (same plane) angles that have a common side and a common vertex (point) but no common interior (inside) points
Next to each other

4. Complementary Angles
Sum of their angles = 90 degrees

5. Supplementary Angles
Two angles that add up to 180 degrees

6. Vertical Angles Two angles whose sides form pairs of opposite rays
Non-adjacent angles formed by intersecting lines.

7. Parallel Lines
Lines on the same plane (coplanar) and do not intersect (cross, touch, meet)
Distance between the two lines are the same. II

8. Vertex
The point where two lines intersect.

9. Perimeter Units around a plane Sum of the length of sides
Distance around an object
Units

10. Acute Angle
Angle whose measure is less than 90 degrees but greater than 0 degrees

11. Obtuse Angle
Angle whose measure is more than 90 degrees and less than 180 degrees.

12. Right Angle
Angle whose measure is 90 degrees

13. Bisect
Divide into two congruent halves
Cut in half

14. Straight Angle Angle whose measure is 180 degrees
Think a straight line

15. Point
A location
No size
Undefined
Point A

16. Line
Undefined
Series of points that extends in two opposite directions
Never ends

17. Collinear Points
Points that lie on the same line

18. Ray Part of a line with one endpoint
One end goes on forever, without end

19. Opposite Rays
Two collinear rays with the same endpoint
Form a line

20. Segment
Part of a line consisting of 2 points

21. Endpoint
Beginning or end of a line segment or ray.

22. Plane Flat surface that has no thickness Has no end
Not collinear points
Plane ABC,
Plane ABCD

23. Coplanar
Points and lines on the same plane

24. Midpoint
Point that bisects (divide) the segment into 2 congruent segments
Point in the middle

25. Angle Bisector
Ray that divides an angle into 2 congruent angles

26. Perpendicular Lines
Two lines that intersect (cross) to form right angles (90 degrees)

27. Perpendicular Bisector
Line, segment or ray that is perpendicular to the segment at its midpoint

28. Congruent Angles
Angles that have the same measure
< AMG ≅ < GMB

29. Congruent Segments
Segments that have the same length ≅

30. Skew Lines
Lines that are NOT parallel, DO NOT intersect, or DO NOT lie on the same plane (noncoplanar)
Line AG is skew to line EB