3rd Class Mathematics Points, Lines and Rays Angles

        A Right Angle

When a straight line stands upright (perpendicular) on another straight line a right angle is formed. In the given figure, a straight line AB stands upright on the another straight line BC thus the ABC is formed is called a right angle. The line AB stands upright on BC called perpendicular line to BC and represented by AB -L BC. A right angle is represented by a box as shown in the figure. The measurement of a right angle is always   (90 degree). In the given figure

Remember the following about a right angle:

• A perpendicular line on another horizontal line forms a right angle.
• The unit for the measurement of an angle is degree (°).
• A right angle is always equal to 90°.
• A square box at the meeting point of two lines represents an angle of90°.
• A perpendicular line between two points is their shortest distance.

Which one of the following options represents a right angle?

(a)  

(b)   

(c)  

(d) All of these  

(e) None of these  

Answer (c)  

Explanation:  A square box at the vertex represents the right angle.      

           Acute Angle

If the measurement of an angle is less than a right angle or 90° then it is called an acute angle. In the figure given below,is less inclined than the angle shown by a square box of right angle. Hence,   is an acute angle.                

               Obtuse Angle

If the measurement of an angle is more than a right angle or  but less than two right angles or  then the angle is called an obtuse angle. In the given figure  is an obtuse angle.