1. Angle Types & Relationships

2. Angle – two rays that meet at a common vertex
Related terminology:
Vertex – the point in space at which two lines, line segments, or rays meet.
Ray – a set of points in the same plane that contains one defined end point and goes on indefinitely in the other direction.
Line – a set of points in the same plane that goes on indefinitely in both directions.
Line segment – a part of a line; a set of points that has two defined end points.
**An angle can also exist as a pair of lines or line segments that meet at a common vertex.**

3. Acute Angle – an angle that measures greater than 0 and less than 90 degrees

4. Obtuse angle – an angle that measures greater than 90 degrees, but less than 180 degrees.

5. Right angle – an angle that measures exactly 90 degrees
Related terminology: ‘perpendicular’……when two lines, line segments, or rays intersect at 90 degree angles, we can say that they are perpendicular to one another.

6. Adjacent angles – angles that share a common vertex and ray
Related terminology: in common language, the word ‘adjacent’ means immediately ‘next to’, so you can think of a pair of adjacent angles as two angles that are right next to one another.

7. Vertical angles – angles that share a common vertex and are formed from the same two lines: they are always congruent
Related terminology: vertical generally means ‘going up & down’, as opposed to horizontal, which means ‘across’; if you are looking at a diagram, a pair of vertical angles can look ‘vertical’, but not necessarily……another way to think of vertical angles is that they are across from one another.
Congruent – ‘equal in measure’

8. Complementary angles – angles whose combined measure equals 90 degrees
Complementary angles do not necessarily have to be adjacent.

9. Supplementary angles – angles whose measures equal a total of 180 degrees
Supplementary angles do not have to be adjacent.

10. I can also say…..
The ‘complement’ of an angle is the amount that would be needed along with that angle to make a total of 90 degrees.
The ‘supplement’ of an angle is the amount that would be needed along with that angle to make a total of 180 degrees.

11. Linear pair – a pair of supplementary angles that are adjacent to one another.