66. Exemplar exercise problems XXXXII

The central angles of two sectors of circles of radii $7 \ cm$ and $21 \ cm$ are respectively $120^\circ$ and $40^\circ$. Find the areas of the two sectors as well as the lengths of the corresponding arcs. What do you observe?

 

When radius $7 \ cm$  and central angle $120^\circ$:

 

Area of sector $=$ $cm^2$

 

Length of the arc $=$ $cm^2$