An angle is a figure formed by two rays that have the same endpoint. The common endpoint
is the vertex of the angle.

An angle that measures greater than 0° but less than 90° is an acute angle

An angle that measures greater than 90° but less than 180° is an obtuse angle

An angle that measures 90° is a right angle

An angle that measures 180° is a straight angle

to determine an angle measure in degrees, you can use a protractor. The mathematical symbol to indicate a degree measure is °.

Angle Relationships

Certain pairs of angles have special relationships. These relationships are useful in determining unknown angle measures. The following sections discuss some of these angle pair relationships.

When the sum of the measurements of two angles equals 90°, the angles are considered complementary.
When the sum of two angles is 180°, the two angles are considered supplementary.

When the sum of the measurements of two angles equals 90°, the angles are considered complementary

When the sum of two angles is 180°, the two angles are considered supplementary

Two angles that have a common vertex and a common side are adjacent angles