Download Types of triangles based on their angles

Geometry Rules
Picture

A
Words
•A
Point A
A
B
Plane B
B
Line AB
AB
B
l
Line
A
Symbols
B
l
l
Ray AB
AB
A
B
Segment AB
AB
Types of angles
Right Angles
A right angle is an angle measuring 90 degrees.
Example: The following angles are both right angles.
Obtuse angle is larger
than 90°
Acute angle is less than 90°
Complementary Angles
Two angles are called complementary angles if the sum of their degree measurements equals 90 degrees.
Example: These two angles are complementary.
Note that these two angles can be "pasted" together to form a right angle!
Supplementary Angles
Two angles are called supplementary angles if the sum of their degree measurements equals 180 degrees.
Example: These two angles are supplementary.
Note that these two angles can be "pasted" together to form a straight line!
Vertical Angles
For any two angles opposite each other at the same vertex when lines that meet, such as in the diagram below,
angle AEB and angle DEC are called vertical angles. Vertical angles have the same degree measurement.
Angle BEC and angle AED are also vertical angles.
Adjacent Angles
For any two angles that are next to each other, such as in the diagram above, angle AEB and angle BEC are
called adjacent angles.
Linear Pair
For any two angles that are next to each other, and the non-common rays are opposite each other forming a
straight line, such as in the diagram above, angle AEB and angle BEC are called a linear pair.
Angle Bisector
An angle bisector is a ray that divides an angle into two equal angles.
Example:
The red ray on the right is the angle bisector of the angle on
The blue ray on the right is the angle bisector
the left.
of the angle on the left.
5”
Find the value of x:
X
15”
X = 15” – 5”, so X = 10”
Find the value of x:
X – 15
Perpendicular
2 lines that meet and form
four right angles.
Parallel
Lines in the same plane, with
the same slope, that never meet.
Congruent
Has the same measure
Collinear
On the same line
Coplanar
On the same plane
2X
X – 15 + 2X = 90°
3X – 15 = 90°
3X = 105°
X = 35°