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.
Right Angle
A right angle is an angle with measure equal to 90 degrees.
Straight Angle
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.
Complementary Angles
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°
Supplementary Angles
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
