Chapter 13 of class 6 results on Interior and Exterior of an Angle, Angles can be either straight, right, acute or obtuse. An angle is a fraction of a circle where the whole circle is 360°. A straight angle is the same as half the circle and is 180° whereas a right angle is a quarter of a circle and is 90°. You measure the size of an angle with a protractor. The figure formed by two rays with the same initial point is called an angle. The common initial point is known as the vertex of the angle, and the rays forming the angle are called its arms or sides. Types of angles are acute angle, obtuse angle, right angle, straight angle, reflex angle, complete angle and zero angles. Clock, compass, arms are examples of angles. The concepts covered include interior and exterior of an angle, the magnitude of an angle and its measurement, units of measuring an angle, various types of angles and much more.