There are 3 half circumferences, one is the top big one, two is the part that's going out, three is the part going inside. We will do the measuring piece by piece.
Circumference formula is [tex]2\pi r[/tex].
The part two has a 9 meters of diameter. If diameter is 9, radius is 4.5 meters. When we plug the values in: [tex]2\pi \times 4.5 = 9\pi[/tex]
But we need to take its half: [tex]\frac {9\pi}{2}=4.5\pi[/tex]
We learned that the part two's length is 4.5π.
Because it has the same diameter, the part three is 4.5π too.
For the last part, we have the radius of 9. When we plug that into the formula:
[tex]2\pi \times 9 = 18\pi[/tex]
Again, we need half: [tex]\frac {18\pi}{2}=9\pi[/tex]
Lastly, add all three pieces: [tex]4.5\pi + 4.5\pi + 9\pi = 18\pi[/tex]
