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 is an angle with measure equal to 90 degrees.
A straight angle is an angle with measure equal to 180 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 degree.
Example: angles a and b with measures a = 19° and b = 71° are complementary since a + b = 90°
Two angles are supplementary if the sum of their measures is equal to 180 degrees.
Example: angles a and b with measures a = 122.1° and b = 57.9° are supplementary since a + b = 180°
Exercises (see solutions below)
Given angles a, b, c, d, e and f with measures
a = 21°
b = 90.1°
c = 90°
d = 134.2°
e = 69°
f = 45.8°
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 References and Links to Geometry TutorialsQuestions on Angles with Solutions and Explanations
Geometry Tutorials and Problems