4th Class Mathematics Geometrical Figures Angle

   Angle

Inclination between two rays having common end point is called angle.

In the above picture, OP and OR are two rays which have a common end point 0. The inclination between the rays OP and OR is called angle POR and it is denoted as . Point O is called vertex and rays OP and OR are called arms of the angle POR.

Features of an Angle

• Angles is measured in degree.
• Symbol of the degree is "°".
• Measure of an angle is written as  a° where a is a number. Ex: 45 degree is written as 45°.

Types of Angles

Angles have been classified into following groups based on their measurement.

• Acute angle
• Right angle
• Obtuse angle

Acute Angle

An angle which is greater than  0°  and smaller than 90°  is called acute angle

Right Angle

An angle of exactly 90° is called right angle .

Obtuse Angle

An angle which is greater than 90° and smaller than 180° is called obtuse angle