Types and Properties of Angles

1. Acute Angle : An angle whose value lies between 0° and 90° is called an Acute Angle.

2. Right Angle : An angle that is equal to 90° is called a right angle.

3. Obtuse Angle : An angle whose value lies between 90° and 180° is called an obtuse angle.

4. Straight Angle : An angle that is equal to 180° is called a straight angle.

5. Reflex Angle : An angle whose value lies between 180° and 360°, is called a reflex angle.

6. Complementary Angle : Two angles are said to be complementary, if their sum is 90° and the complementary angles are complement of each other. Complement of θ is () 90° − θ.

7. Supplementary Angles : Two angles are said to be supplementary, if their sum is 180° and the supplementary angles are supplement of each other.

Regular Polygon

Polygon : A simple closed curve made up of three or more line  segments is called a polygon. 

Regular Polygon : If the length of all the sides and all angles are equal, then, it  is called regular polygon.  Some important facts related to polygon are as follow  

• Polygon with three sides is called triangle. 
• Polygon with four sides is called quadrilateral. 
• Polygon with five sides is called pentagon. 
• Polygon with six sides is called hexagon. 
• Polygon with seven sides is called heptagon. 
• Polygon with eight sides is called octagon. 
• Polygon with nine sides is called nonagon. 
• Polygon with ten sides is called decagon.