Answer:
[tex] \boxed{ \boxed{ \bold{ \purple{16.485 \: cm}}}}[/tex]
Step-by-step explanation:
Diameter ( d ) = 21 cm
Radius is just half of the diameter
Radius ( r ) = [tex] \sf{ \frac{21}{2} }[/tex] = 10.5 cm
Now, let's find the perimeter of a semi - circle :
[tex] \sf \frac{1}{2} \pi \: r \: [/tex]
Plug the values
⇒[tex] \sf{ \frac{1}{2} \times 3.14 \times 10.5}[/tex]
Calculate
⇒[tex] \sf{16.485 \: cm}[/tex]
Hope I helped!
Best regards!
