1. Geometry Vocabulary

2. Why Learn Vocabulary?
It is important to know the vocabulary to be able to communicate and understand the questions you come across.

3. Point A point is a position in space represented by a dot
usually named with a capital letter.
A point can’t be measured because it has no length and no height. 

4. Line
A line is represented on a diagram by a straight line with arrows on both ends.
has no width and extends infinitely in both directions.
It take two points to define a line
an infinite number of points are on the line.

5. Line It is named with two of the points on the line
or with a lowercase italicized letter. ,
and line k are the same in the diagram.

6. Ray A ray is part of a line.
It starts at one point and goes infinitely in one direction.
starts at point B and goes through point D and continues forever in that direction.
is not the same ray.

7. Segment A segment is between two points.
is the segment between point A and point B.
Notice the part of ray that is the same as part of ray is segment  

8. Intersection An intersection is where geometric objects share space.
Two lines intersect at a point.
Line k and line m intersect at point B.
is the intersection of and  

9. Angle and Vertex Two rays with a common starting point form an angle.
The common point is called the vertex.
An angle may be named by it's vertex when the vertex alone is not ambiguous.
Three points can also designate an angle with the vertex as the middle point
Angles might also be numbered

10. Perpendicular Perpendicular lines intersect at 90 degree angles.
is read line CE is perpendicular to line BD.

11. Parallel Parallel lines don't intersect,
No matter how far the lines are extended
Line k is parallel to line m but is not parallel to line n. 

12. Acute angle An acute angle is less than 90 degrees. is acute.
Think "a cute little angle" to remember the term.

13. Obtuse angle An obtuse angle is greater than 90 degrees is obtuse.
Think "obtuse angles are wide angles to remember.

14. Right angle A right angle is exactly 90 degrees. and are right angles.
The little square at the vertex indicates the angle is 90 degrees.

15. Complementary angles Complementary angles add to 90 degrees
are complementary angles.

16. Supplementary angles Supplementary angles add to 180 degrees
are supplementary angles.

17. Vertical angles
Vertical angles are across the intersection of two lines from each other.
and are vertical angles.
Vertical angles are equal.
There are two pairs of vertical angles in one intersection.

18. Vertical angles
Vertical angles are across the intersection of two lines from each other.
and are vertical angles.
Vertical angles are equal.
There are two pairs of vertical angles in one intersection.

19. Warm Up Classify each angle as acute, obtuse, or right. 1. 2. 3. right 3.
right
acute
obtuse

20. Objectives
Classify triangles by their angle measures and side lengths.
Use triangle classification to find angle measures and side lengths.

21. Vocabulary acute triangle equiangular triangle right triangle
obtuse triangle
equilateral triangle
isosceles triangle
scalene triangle

22. Recall that a triangle ( ) is a polygon with three sides
Recall that a triangle ( ) is a polygon with three sides. Triangles can be classified in two ways: by their angle measures or by their side lengths.

23. C A B AB, BC, and AC are the sides of ABC.
A, B, C are the triangle's vertices.

24. Acute Triangle Three acute angles Triangle Classification
By Angle Measures
Acute Triangle
Three acute angles

25. Three congruent acute angles
Triangle Classification
By Angle Measures
Equiangular Triangle
Three congruent acute angles

26. Right Triangle One right angle Triangle Classification
By Angle Measures
Right Triangle
One right angle

27. Obtuse Triangle One obtuse angle Triangle Classification
By Angle Measures
Obtuse Triangle
One obtuse angle

28. Obtuse Triangle One obtuse angle Triangle Classification
By Angle Measures
Obtuse Triangle
One obtuse angle

29. Equilateral Triangle Three congruent sides Congruent means equal
By Side Lengths
Equilateral Triangle
Three congruent sides

30. At least two congruent sides
Triangle Classification
By Side Lengths
Isosceles Triangle
At least two congruent sides

31. Scalene Triangle No congruent sides Triangle Classification
By Side Lengths
Scalene Triangle
No congruent sides