Angles in Geometry
Definitions and properties of angles in geometry.
An Angle in Geometry
An angle is the rotation required to superimpose one of two intersecting lines on the other.
A Right Angle
A right angle is an angle with measure equal to 90 degrees.
An Acute Angle
An acute angle is an angle with a measure between 0 and 90 degrees.
An Obtuse Angle
An obtuse angle is an angle with a measure between 90 and 180 degrees.
Two angles are complementary if the sum of their measures is equal to 90 degrees.
Example: angles a and b with measures a = 19o and b = 71o are complementary since a + b = 90o
Two angles are supplementary if the sum of their measures is equal to 180 degrees.
Example: angles a and b with measures a = 122.1o and b = 57.9o are supplementary since a + b = 180o
Exercises (see solutions below)
Given angles a, b, c, d, e and f with measures
a = 21o
b = 90.1o
c = 90o
d = 134.2o
e = 69o
f = 45.8o
1 - Which of these angles are acute?
2 - Which of these angles are obtuse?
3 - Which pairs of angles are complementary?
4 - Which pairs of angles are supplementary?
Solutions to Above Exercises
1 - a, e and f
2 - b and d.
3 - a - e
4 - d - f
More geometry references
Geometry Tutorials, Problems and Interactive Applets.