
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.
Complementary Angles
Two angles are complementary if the sum of their measures is equal to 90 degrees.
Example: angles a and b with measures a = 19^{o} and b = 71^{o} are complementary since a + b = 90^{o}
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^{o} and b = 57.9^{o} are supplementary since a + b = 180^{o}
Exercises (see solutions below)
Given angles a, b, c, d, e and f with measures
a = 21^{o}
b = 90.1^{o}
c = 90^{o}
d = 134.2^{o}
e = 69^{o}
f = 45.8^{o}
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.

