Question

Draw the following angle using ruler and compasses. Also label them.
${120}^o$

Answer 1

An angle of ${120}^{\circ }$ is nothing but twice of an angle of ${60}^{\circ }$.Therefore, it can be constructed as follows :

Step $1:$ Draw any line $PQ$ and take a point $O$ on it.

Step $2:$ Place the pointer of the compasses at $O$ and draw an arc of convenient radius which cuts the line at $A$.

Step $3:$ Without disturbing the radius on the compasses, draw an arc with $A$ as centre which cuts the first arc at $B$.

Step $4:$ Again without disturbing the radius on the compasses and with $B$ as centre, draw an arc which cuts the first arc at $C$.

Step $5:$ Join $OC$, $\angle COA$ is the required angle whose measure is ${120}^{\circ }$.