Geometry 1.4 - World of Angles

I will try to define the different types of angles that you will face in geometry class, leaving out the more technical words.

Types of Angles:

(1) Acute - any angle which measures less than 90 degrees.

Example: The angle ABC measures 40 degrees. Angle ABC is acute.

(2) Right - any angle which measures exactly 90 degrees.

Sample: The angle CAT measures 90 degrees. The angle CAT is a right angle.

(3) Obtuse - any angle which measures more than 90 degrees but less than 180 degrees.

Sample: angle DEF measures 125 degrees. Then angle DEF is obtuse.

(4) Straight - any angle which measures exactly 180 degrees.

Sample: Points ABC lie on line L forming a STRAIGHT LINE. Then line L is a straight line.

(5) Vertical Angles - Two angles formed by intersecting lines. They can not be adjacent but are always equal in measure. They are across from one another in the corners of the "X" formed by the lines.

In the above picture, angles 1 and 3 and angles 2 and 4 are vertical because they are across from each other. Now, angles 1 and 2 and angles 3 and 4 are NOT vertical angles.

(6) Complementary Angles - Two angles whose measures add up to 90 degrees.

Sample: angle A = 30 degrees and and angle B = 60 degrees.
Then angle A + angle B = 90 degrees. We can say angles A and B are complementary.

(7) SupplementaryAngles - Two angles whose measures add up to 180 degrees. Supplementary angles can be placed so that they form a straight line.

Sample: angle A = 80 degrees and angle B = 100 degrees. Then angle A + angle B = 180 degrees. We can say that angles A and B are supplementary.